CHAPTER 8
Diagnostic Tests and What They Mean
A diagnosis of irritable bowel syndrome can be made by any of several types of medical practitioners and with fewer or more tests, depending on what symptoms the person is experiencing. Some patients are diagnosed with IBS by their primary care provider after a careful history is taken, the symptoms are reviewed, and a physical examination is performed and doesn’t reveal another cause for the symptoms, as described in Chapter 7. Other patients are diagnosed with IBS only after they have been referred to a specialist for evaluation. Typically, that specialist is a gastroenterolo-gist: a physician who, after finishing four years of medical or osteopathy school, undertakes a three-year training program in internal medicine and then completes an additional three or four years of specialized training in gastroenterology, the study of the digestive tract and the internal organs associated with digestion. Gastroenterologists are well versed in treating people who have IBS.
During the evaluation of a patient who has IBS, doctors and other practitioners sometimes perform diagnostic studies or tests. These tests may be done because information gleaned from either the patient’s history or the physical examination makes the physician suspect that there may be another condition causing the symptoms. For example, a middle-aged woman who has symptoms of IBS and constipation and states that she feels cold all the time and that she has noticed a change in her voice may have a thyroid disorder. A patient who has abdominal discomfort and diarrhea may indeed have IBS, but these symptoms could also be signs of an infection in the colon. In this situation, the provider would request that samples of stool be collected and analyzed to check for an infection.
In the evaluation of a patient who has symptoms of IBS, some tests are fairly simple, such as having a sample of blood drawn for blood tests. Others are a little more complicated, such as getting a CT scan of your abdomen. Some tests are more invasive, such as flexible sigmoidoscopy or colonoscopy. Occasionally, patients will have persistent symptoms that fail to respond to dietary interventions or medical therapy. Such patients are referred to large hospitals or academic medical centers for sophisticated tests that might include anorectal manometry and defecography (video or magnetic resonance).
It is surprising to many people that experts in the field still disagree quite a bit about what tests should be used in the evaluation of a patient who has IBS symptoms. Some doctors believe that no tests are required for a young person who has classic symptoms of IBS, as long as the history and physical examination are completely normal and the warning signs (“red flags”) of more serious diseases with similar symptoms have been carefully looked for. Other doctors believe that all patients should have certain simple tests to exclude other conditions, that is, to make sure that another problem is not masquerading as IBS. These tests would probably include some simple blood tests and either flexible sigmoidoscopy or colonoscopy. Another approach is to go ahead and begin treatment if a patient has classic symptoms of IBS and no warning signs of other conditions and to have tests done only if the patient does not improve with treatment. Finally, some doctors believe that IBS is a “diagnosis of exclusion,” that it can only be diagnosed after other possible causes have been eliminated with a battery of tests, all producing normal results.
Several studies have looked at the value of performing certain laboratory or diagnostic studies in the evaluation of patients who have IBS symptoms. In one study, when more than 1,400 people with symptoms of IBS underwent laboratory tests and diagnostic studies, the rate of significant medical problems was the same in the people who had IBS symptoms and in the control (or comparison) group of healthy volunteers who did not have IBS symptoms. More specifically, when the group with IBS symptoms had blood work done to look for anemia (“low blood count”), infection, thyroid disease, or evidence of inflammation in the body, all of their tests were as normal as the group of healthy volunteers. Furthermore, when the patients who had IBS symptoms were given specialized tests for lactose intolerance and a problem in the colon, once again the results were no different from the healthy volunteers. Thus, if people who have IBS symptoms keep coming up with the same test results as people who do not have those symptoms, one wonders how useful it is to put the patient through the trouble and expense of the tests. A recently published study from several major medical centers in the U.S. confirmed these results and also found that celiac disease was not more prevalent in people who had IBS than in people who were undergoing routine screening colonoscopy. There are currently no firm guidelines about which tests need to be routinely performed in the course of evaluating patients who have symptoms of IBS. For this reason, I’ll review some of the most commonly recommended tests that your health care provider may discuss with you (Table 8.1). My own recommendations are given at the end of the chapter. Below we look in some detail at each of the tests mentioned above.
Laboratory Tests
The tests described below are all performed by having a blood sample drawn, which may be done in an outpatient laboratory or clinic or by your doctor or another practitioner in the doctor’s office.
Complete Blood Count (CBC)
A complete blood count, usually called a CBC, measures many items of interest. The two items of most significance in the diagnosis of IBS are your red blood cell count, to see if you are anemic, and your white blood cell count, looking for evidence of an infection. White blood cells help you fight an infection when it has gotten into your body. A normal white cell count ranges from 3,500 to 10,000 (commonly abbreviated as “3.5–10”) white blood cells per microliter (one millionth of a liter) of blood. If you have an infection, your white blood cell count (WBC) is typically elevated. With IBS the WBC should be normal, since the GI tract is not infected, unless you have an elevated WBC as the result of another problem occurring at the same time. Thus, in a person with abdominal pain and diarrhea, an elevated WBC may indicate that the symptoms are being caused not by IBS but rather by another ailment, such as inflammatory bowel disease (IBD) or a bacterial infection in the colon.
Table 8.1. Tests Frequently Used in the Evaluation of Patients Who Have IBS Symptoms
Noninvasive tests
Blood tests: CBC, electrolytes, ESR, TSH, LFTs
Stool tests: fecal occult blood, stool cultures, O&P
X-ray tests: UGI series, barium enema, sitz marker study, CT scan
Invasive tests
Endoscopy: sigmoidoscopy, colonoscopy |
The other important piece of information to look for in a CBC is whether or not you are anemic. Anemia refers to a low red blood cell count. This is determined by checking the hemoglobin (abbreviated Hgb) and hematocrit (Hct). Hemoglobin is a protein found in red blood cells; it chemically binds to oxygen and carries the oxygen through your bloodstream. Women typically have hemoglobin levels of 12 to 16 mg/dl (dl means “deciliter,” about 3.4 oz), while normal hemoglobin levels in men are 14 to 18 mg/dl. Your hematocrit is the percentage of red blood cells in a sample of your blood. Hematocrit levels in women typically range from 37 to 47 percent, and in men these levels are usually slightly higher, at 42 to 54 percent. If you are anemic, your red blood cell count is typically lower than the norms described above. There are many causes for anemia, including not making enough red blood cells, losing red blood cells (by bleeding) somewhere in the body, or premature destruction of red blood cells (red blood cells typically last 120 days in the bloodstream, and new ones are constantly being made in the bone marrow). By definition, IBS does not cause anemia. Patients can certainly have IBS and be anemic for other reasons (for instance, low iron intake, poor absorption of vitamin B12, very heavy menstrual cycles, recurrent bleeding from elsewhere in the body). If anemia turned up during evaluation for IBS, it would need to be investigated.
Thyroid Stimulating Hormone (TSH)
The thyroid is a small gland in the front of the neck, shaped almost like a butterfly. It is responsible for producing thyroxine, a hormone that acts throughout the body and helps to regulate metabolism. Approximately 6 percent of people in the United States have problems with their thyroid. This percentage is not higher among people who have IBS. In some people the thyroid is overactive; these persons may feel anxious or jittery, lose weight unintentionally, notice changes in their vision, and have diarrhea. People who have an underactive thyroid may gain weight unintentionally, notice a deepening of their voice, feel sluggish or tired, and have problems with constipation. Many physicians routinely check TSH levels in patients who have chronic constipation or diarrhea, to determine whether the thyroid gland is a factor in their bowel patterns. If your level of thyroid stimulating hormone is abnormal, your doctor may refer you to a specialist called an endocrinologist.
Erythrocyte Sedimentation Rate and C-Reactive Protein
Many patients and their doctors are concerned that the symptoms of IBS, especially diarrhea, may indicate an inflammatory process in their intestinal tract. Many health care providers will therefore check the patient’s erythrocyte sedimentation rate (ESR). This simple blood test is a reasonable (although not perfect) measure of inflammation and infection in the body. For the same purpose, other doctors check for C-reactive protein (CRP). It is important to note that neither of these tests reveals where the inflammation or infection is. Rather, both the ESR and the CRP simply give evidence that some portion of the body is inflamed or infected. A common cold will increase a person’s ESR and CRP, as will an infected toe or an inflamed joint. Because with irritable bowel syndrome the intestinal tract is not chronically inflamed or infected, patients who have IBS should have normal ESR and CRP levels, unless there is inflammation or infection present from another cause. If either of these levels is high, your doctor may need to order other laboratory tests or schedule special studies to help find out why.
Electrolytes and Kidney Function Tests
Electrolytes are salts (sodium, potassium, and chloride) in your blood. Kidney function tests (blood urea nitrogen [BUN] and creatinine) measure how well your kidneys work—how well they filter your blood of toxins and whether they can produce urine normally. These two types of tests should be normal in patients who have IBS. Some doctors routinely order these tests, while other doctors use them only for people who have recurrent or prolonged diarrhea, to make sure that the patient is not becoming dehydrated. Again, patients can have IBS and also abnormal kidney function and abnormal electrolytes, but IBS by itself should not affect these levels.
Liver Function Tests (LFTs)
The term liver function tests refers to several separate blood tests, usually performed as a group, that measure the level of specific enzymes within the liver. Enzymes are chemicals that speed up chemical reactions within the body. Their presence in the blood increases if there is an infectious or inflammatory process in the liver, such as hepatitis, or there is obstruction of the ducts draining the liver, as with gallstones. The liver is not associated with IBS in any way. However, some patients who have IBS have abdominal pain or discomfort in the upper abdomen near the liver. For that reason, many providers check LFTs to make sure that the abdominal pain or discomfort does not reflect some underlying problem in the liver. If these tests show elevated enzyme levels, your doctor may schedule a special x-ray study of your liver (either an ultrasound or a CT scan) and may refer you to a specialist in liver disorders, a hepatologist.
Stool Studies
Three stool studies are commonly ordered by doctors during the evaluation of a patient who has altered bowel habits and abdominal pain. The first is a stool heme-occult test. The second is a group of studies that look for an infection in the colon. The third test is a specialized test for evidence of inflammation in the colon.
The heme-occult test is a simple test used to look for nonvisible (occult) blood (heme) in the stool. This test can be performed in your doctor’s office, or your doctor may give you specially treated cards so you can perform this test at home. Testing for occult blood in the stool is often routinely done for patients over age 50 as a “screening” test for colorectal cancer. (A screening test is one that detects a medical problem early on in its course, so that it can be quickly treated to prevent a more serious condition from developing.) People who have persistent diarrhea are often tested for occult blood, because the diarrhea may indicate an inflammatory condition, such as Crohn’s disease, that could cause the person to slowly lose blood. Heme-occults are also frequently performed for patients who have abdominal pain and constipation, because of the concern that the constipation is a sign of cancer of the colon or rectum. People who have cancer of the colon often become anemic because the growing cancer may slowly bleed. The blood shows up in the stool, giving a positive (“positive” in medical terms means that the substance being looked for is present, not that the result is good) heme-occult result.
The advantages of the heme-occult test are its simplicity, ease, safety, and low cost. The major disadvantage is that it is not very accurate. The test may give misleading results. It may show that blood is present even though no disease is there. On the other hand, the test may be negative—not showing the presence of blood—when there actually is a problem. In a variety of disorders of the colon (a polyp, an early cancer, inflammation) bleeding can be intermittent (come and go). Thus, on the day the stool sample is checked, the test may be negative (that is, no blood is present) if there has been no recent bleeding, but on another day it would be positive. Because heme-occult tests can miss serious disorders such as colon cancer, nearly all gastroenterologists recommend that everyone over the age of 50 undergo a screening colonoscopy to look for cancer of the colon or rectum. Due to an increased risk of colon cancer in African Americans, gastroenterologists now recommend that routine colon cancer screening start at age 45 for African Americans.
If there is evidence of blood in your stool, your doctor will probably suggest that you get a complete blood count, if one hasn’t recently been performed. In addition, he or she will probably advise that you have either a flexible sigmoidoscopy or, in most cases, a colonoscopy (both described below).
The second most commonly ordered stool study is a panel of tests designed to look for evidence of an infection in the colon. If you have persistent diarrhea, your doctor may recommend that samples of stool be collected and sent to a laboratory to be tested for evidence of an infection. One test determines if there are fecal leukocytes in the stool. Leukocytes are white blood cells. People who have an infection or inflammatory process in the colon generally have a large number of white blood cells (fecal leukocytes) in their stool. If this test is normal (that is, no white blood cells are seen), then your doctor may not need to order any more stool studies, as it is very unlikely that you have an inflammatory or infectious condition in your colon. Patients who have IBS and diarrhea normally do not have fecal leukocytes in their stool, while with patients who have Crohn’s disease, ulcerative colitis, or some kind of infection in their colon, large numbers are generally found in the stool. If your stool studies return showing that you have a high number of fecal leukocytes, your doctor may order additional stool studies, looking for common infections of the colon (Salmonella, Shigella, Campylobacter, Yersinia, and Clostridium difficile) or the presence of parasites (the O&P test, meaning “ova and parasites”). Giardiasis is a common parasitic infection (caused by Giardia) that can produce symptoms of abdominal discomfort and diarrhea that mimic the symptoms of IBS.
A new and, as yet, seldom performed study tests for lactoferrin in the stool of patients who have chronic diarrhea. This chemical is found much more commonly in the stool of people with an inflamed colon than in healthy people or patients who have IBS, so its presence could signal either inflammatory bowel disease or an infection.
Endoscopy
Endoscopy refers to any type of procedure that uses a thin, flexible, lighted tube to view the inside of the gastrointestinal tract. These tubes, called endoscopes (more specifically, sigmoidoscopes and colonoscopes), have both a light and a miniature video camera inside. In addition, endoscopes have thin channels that permit the passage of tiny forceps, with which the operator can take samples of tissue (biopsies) to be tested in a laboratory, if necessary.
In an upper endoscopy, the upper GI tract (esophagus, stomach, and duodenum) is examined using an endoscope. Endoscopies of the lower GI tract examine the colon and anorectal area. Patients who have IBS and either diarrhea or constipation are often referred to a gastroenterologist or a surgeon for endoscopy of the lower GI tract, either a sigmoidoscopy, which looks at the anorectal area, sigmoid colon, and descending colon, or a colonoscopy, which extends the examination to the full length of the colon. Both tests are usually performed in an outpatient setting; they can be done in a hospital, but they do not require an overnight stay. Both examinations are designed to allow your doctor to look directly at the lining of your lower intestine and rectum. They can be used to search for sources of bleeding, for evidence of an obstruction or blockage, or for the presence of diverticuli (abnormal pockets or pouches in the intestine), polyps, and cancerous tissue. These examinations are very helpful in revealing the presence of either an infection or inflammatory bowel disease. During endoscopy, the lining of the intestinal tract is clearly seen and can be carefully inspected. Photographs can be taken, either to document a problem or to provide a baseline so that a subsequent test can be compared to the conditions during the first test. If necessary, biopsies can be taken and polyps can be removed.
For both sigmoidoscopy and colonoscopy you need to prepare by taking medications or solutions to “clean out” the colon. This preparation is usually done the day before the test. With some methods of preparation, you may also be asked to consume only clear liquids for one or two days before the test or to work your way down in steps from solid food to clear liquids during a period of two to three days.
On the day of the exam, you will need to arrive an hour or two before the test. A nurse will check you in, and the physician performing the test, if it is not your own gastroenterologist, may take a brief history and do a limited physical examination. The endoscopy is usually performed in a special room. You will lie on your left side (on your left shoulder and left hip) with your right knee partially bent and brought toward your chest. The physician will perform a digital rectal examination before beginning to insert the endoscope.
Flexible Sigmoidoscopy
Sigmoidoscopy uses a shorter endoscope than colonoscopy. Because of that, the examination is limited to the lower colon and rectum, which includes the anal canal, the rectum, the sigmoid colon, and the descending colon (see Figure 8.1). On some occasions, depending on the patient’s anatomy and level of comfort, the endoscope can be advanced past the splenic flexure and into the transverse colon, although this does not routinely occur. The test generally takes anywhere from 5 to 20 minutes, depending on the patient’s anatomy, the patient’s comfort, and whether or not biopsies need to be taken or polyps need to be removed. In contrast to colonoscopy (described below), flexible sigmoidoscopy is usually performed without sedation. This means that there is very little recovery time after the procedure; most patients can resume their regular activities, including driving a car, immediately afterward. Not using sedation also decreases the risks associated with the procedure.
Figure 8.1. Flexible Sigmoidoscopy
Flexible sigmoidoscopy is performed to allow the doctor to see the lining of the lower gastrointestinal tract. The sigmoidoscope is a soft, flexible, lighted tube that is inserted through the anal canal and rectum and carefully advanced through the sigmoid colon and descending colon. Under ideal conditions, the sigmoidoscope can be advanced to the splenic flexure. This test is usually performed in an outpatient setting. If necessary, biopsies can be taken and polyps can be removed with tiny forceps inserted through the end of the sigmoidoscope. Reasons for having this test include rectal bleeding, rectal pain, chronic diarrhea, and lower abdominal pain thought to arise in the GI tract.
Flexible sigmoidoscopy begins with the patient lying on her or his left side, with the right knee drawn up toward the chest. As described above, a rectal examination is performed first. During this initial part of the examination, you may have the feeling that you need to have a bowel movement. This is a normal sensation that occurs due to stimulation of nerves in the rectum. The sigmoidoscope is then gently inserted and carefully advanced to its fullest extent—usually the upper portion of the descending colon, near the splenic flexure. The sigmoidoscope is then slowly withdrawn, and the physician carefully watches the images of the colon displayed on a large video screen. In most endoscopy procedure rooms, the patient is also able to watch these images if he or she desires.
During this part of the procedure, the endoscopist may need to add a little air to your colon, a process called insufflation, because the colon, being empty, is typically collapsed. Inserting air into the colon enables the physician to better visualize its lining. You may feel some pressure in your abdomen when the air is introduced and may have some mild abdominal discomfort or cramps as the scope goes around a curve or bend in your colon, but most patients tolerate flexible sigmoidoscopy quite well. Although the air is removed at the end of the procedure as completely as possible, some patients feel a little bloated or gassy after the test. Some patients feel mild abdominal discomfort, which is usually caused by a spasm of the smooth muscle that makes up the lining of the colon. This spasm can occur in response to stretching of the colon, either by the air that is placed into the colon or by the endoscope. These sensations are unpleasant for some patients, but they rarely mean that anything significant is happening.
At the end of the procedure, which on average takes about 10 minutes, you can get dressed, and a nurse will check you before you leave. The doctor will be able to share the results of the visual examination with you right away, but if biopsies were taken or polyps removed, the pathology test results will take 5 to 10 days. No special diet is required after flexible sigmoidoscopy; you can return to your regular diet following completion of the test.
Colonoscopy
Because colonoscopy uses a much longer endoscope compared to flexible sigmoidoscopy, the entire colon can be carefully examined (see Figure 8.2). Often, we can even see the end of the small intestine (terminal ileum) and the area where the small intestine and colon connect (ileocecal valve), areas that are important if your doctor is concerned that you might have inflammatory bowel disease.
Another advantage of colonoscopy is that it is generally performed using mild sedation. This means that most patients either sleep through the exam or are partially awake but relaxed and quite comfortable. During “conscious sedation,” you breathe on your own, and your vital signs (blood pressure, heart rate, oxygen content of your blood, respiratory rate) are constantly measured. Conscious sedation is considered very safe; it is quite different from general anesthesia, in which the patient is connected to a ventilator (breathing machine), sleeps deeply, and takes a long time to recover from the sedation.
Colonoscopy is considered the most effective screening test for colorectal cancer and is recommended for everyone over the age of 50 (although, as noted above, screening colonoscopies should start at age 45 in African Americans). Compared to sigmoidoscopy, the preparation is usually a little longer and somewhat more involved. In addition, due to the use of sedation, recovery time is longer, and you will not be allowed to drive until the following day. You will not be able to go to school or work after the test, because your thinking might be foggy from the sedation and your legs might be a little wobbly. Finally, because the test examines your entire colon, the risk of having a complication is slightly greater than in sigmoidoscopy.
Colonoscopy begins just like flexible sigmoidoscopy, with one major exception. Prior to the test, an intravenous (i.v.) catheter will be inserted into a vein in one of your arms. This is a thin needle connected to plastic tubing so that medications can be administered during your examination.
As with flexible sigmoidoscopy, the colonoscope is gently inserted and advanced, this time through the entire colon. If your doctor is concerned about the possibility of IBD (Crohn’s disease or ulcerative colitis), then he or she will also inspect the lower small intestine (the terminal ileum). As the colonoscope is slowly withdrawn, the physician will likely need to add some air to the colon, as described above, to make sure that she or he can get a good look at the lining of the colon. If necessary, biopsies can be taken or polyps removed.
Figure 8.2. Colonoscopy
The colonoscope is just like the sigmoidoscope (see Figure 8.1), only longer. It enables viewing of the entire colon. Colonoscopy is usually performed using “conscious sedation,” since the test takes longer and is more uncomfortable for some patients than sigmoidoscopy. As with sigmoidoscopy, if necessary, biopsies can be taken and polyps removed during the exam.
The doctor is able to learn a great deal by visual examination of the entire colon, and he or she will probably mention the findings to you after you are awake; but because you may be groggy from the sedation, a follow-up visit or phone conversation may be scheduled. If biopsies were taken, the pathology report on them will not be available for 5 to 10 days, and your doctor will review those results with you then.
Risks
Both of these examinations are considered very safe, and in the overwhelming majority of cases, the benefits far outweigh the possible risks. However, some minor reactions or side effects can occur with either test, such as irritation of the colon, nausea or vomiting shortly after the exam, or a persistent feeling of being bloated or gassy due to the introduction of air into the colon. As with any medical procedure, there is the possibility that some more serious unintended consequence could occur. The colon could bleed significantly, although this is usually a possibility only if a large polyp is removed during the procedure.
Perforation, where a hole is inadvertently made through the wall of the colon, although a real possibility, is very uncommon. It occurs in less than 1 in 3,000 procedures. If a perforation occurs, it can often be safely managed by admitting the patient to the hospital, giving intravenous fluids and antibiotics, and letting the bowel rest and repair itself.
Colonoscopy carries risks that are due to the use of sedation. The medications used to aid relaxation during the procedure can result in deeper sedation than expected, necessitating a longer recovery time, possibly admission to the hospital, the use of medications to “reverse” the sedating medications, or, very rarely, use of a ventilator to assist breathing.
Radiologic Studies
CT Scan of the Abdomen
Computed tomography (CT) scans use a small amount of radiation from a special scanner, combined with sophisticated computer software, to provide precise cross-sectional images of the body. This imaging technique is often performed for patients who have chronic abdominal pain, to look for problems that can’t be detected using blood tests and to look in places inside the body that can’t be viewed by endoscopy (upper endoscopy or colonoscopy). Usually, patients drink a special liquid before the test (called oral contrast) that coats the intestinal tract. A second type of contrast agent is usually injected through an intravenous (i.v.) catheter into a vein in your arm (intravenous contrast). These two different contrast agents enable the physician reading the study (a radiologist) to clearly identify the GI tract and the surrounding blood vessels (arteries and veins). Although this is a noninvasive test, use of the second contrast agent requires that an i.v. line be placed, which some patients find uncomfortable. The test typically takes three hours, which includes the time needed to drink the contrast and to have the i.v. catheter put in. No sedation is used during a CT scan. The results are usually available within 24 hours.
Upper GI Series
This examination allows evaluation of the structure, and provides some information regarding the function, of the upper gastrointestinal tract (esophagus, stomach, pylorus, and duodenum). It is usually performed in the morning after an overnight fast (no food or fluid after midnight). Patients swallow approximately 2 cups (16 oz.) of an oral contrast, usually a barium solution. (Barium is an inert [nonreactive], chalky white substance that shows up vividly on x-ray images.) The barium solution coats the lining of the GI tract, and then x-ray pictures are taken over the next 30 to 45 minutes. On some occasions, the x-ray pictures are taken during a longer period of time, 2 to 3 hours. This longer time period allows the contrast solution to pass all the way through your small intestine, so that images can be made of this area as well (this test is called an upper GI series with small bowel follow-through).
This test is noninvasive, does not require an intravenously injected contrast agent or any sedation, and is safe. It can provide significant amounts of information about the anatomy and structure of the upper GI tract. Your doctor may order this test if she or he is concerned that you have an ulcer or blockage of the GI tract. Results of this test are generally available within 24 hours.
Sitz Marker Study
This test measures how long it takes for material to move through the colon. As such, it is an indirect measure of colonic transit time and colonic motility. It may be requested for patients who have constipation, especially those who are not responding to treatment. Patients swallow a gelatin capsule that contains 24 small, spherical, radio-opaque markers. Because these markers are radio-opaque, they show up on x-ray images (this test may also be called a “radio-opaque marker study”). These tiny markers do not dissolve in your gastrointestinal tract but are transported from the stomach to the small intestine and into the colon by peristalsis. They are normally evacuated along with stool anywhere from 1 to 5 days after being swallowed. We recommend that the capsule be taken on a Sunday morning. You then go to the radiology department 1, 3, and 5 days later for a simple abdominal x-ray, until the markers have been evacuated. These x-rays should be taken at approximately the same time of day that the capsule was swallowed. The location and the number of the markers are noted on each of the days, and this provides a good estimate of how fast, or how slowly, contents move through your colon and sometimes can show where they slow down or get hung up. Normally, at least 20 of the 24 markers are eliminated from the colon by the fifth day.
Overall, this is a very safe and easy test. Disadvantages include that you have several x-rays taken of your abdomen, which means that you receive a small amount of radiation each time. However, this amount of radiation is generally considered safe. If you live a long distance from a radiology clinic, the repeated visits can be inconvenient, but patients usually find the effort worthwhile. No sedation is needed for this test. Results of this study are typically available to the ordering physician within 24 hours after the last x-ray is taken.
Other Tests
Ultrasound of the Abdomen and Pelvis
Ultrasound imaging uses sound waves, organized by a computer, to create pictures of internal organs. A small device, approximately the size of a hand-held microphone, is placed on your skin over the area to be scanned. Sound waves are then transmitted through the skin and a recording is made as these sound waves are reflected by the organs. Ultrasound can produce a three-dimensional picture of the liver, gallbladder, pancreas, kidneys, uterus, and ovaries. These pictures can reveal the size and shape of each organ and can show the presence of an obstruction, cysts (fluid-filled pockets), or a solid mass, such as a tumor.
The advantages of ultrasound include that it is noninvasive, very safe, does not expose the patient to any radiation, and does not require sedation. It may require drinking large amounts of water and not going to the bathroom for a couple of hours, which can be uncomfortable for some people. Unfortunately, it cannot measure the function of an organ and it is not that helpful in evaluating the structure of the gastrointestinal tract. Results of ultrasound imaging are usually available within 24 hours.
Hydrogen Breath Test
People with bloating and gassiness occasionally have a medical condition that prevents them from properly digesting certain types of food, most commonly the sugars lactose and fructose. In an unusual condition that can also cause chronic gassiness, too many bacteria exist in the upper gastrointestinal tract. Although the colon is loaded with bacteria, there should be only a very small amount of bacteria in the small intestine. If you are having trouble digesting certain types of sugars, or if your doctor is concerned that you may have bacterial overgrowth, then a hydrogen breath test may be recommended (see Chapter 11).
This safe and easy test is usually performed in the morning after an overnight fast. Patients drink a small amount of a sugary liquid (lactulose, fructose, or lactose) and then blow into a special measuring device every 15 minutes during a period of about 3 to 4 hours. The amount of hydrogen in the expelled air is measured, and this can help determine whether one of the conditions noted above is the cause of the gas and bloating. The captured samples of exhaled air are sent to a laboratory for analysis. The results of the analysis are usually available within 2 to 3 days. If the results are positive, indicating that you have too many bacteria in your small intestine, your physician may decide to treat you with antibiotics.
Anorectal Manometry (ARM)
This test may be recommended for patients who have persistent severe constipation or who have experienced fecal incontinence. Fecal incontinence, the accidental leakage of stool from the rectum, may develop as a result of injury to the muscles or nerves in the pelvic floor or because of disease. Anorectal manometry is designed to evaluate muscle and nerve function in the anal canal, rectum, and pelvic floor (see Figures 6.1–6.3). It is generally available only at major medical centers and in large hospitals or clinics interested in research. Patients lie on their left side on an examining table and a small balloon attached to a tube is inserted into the anal canal and rectum. The patient is asked to contract specific muscles in the anorectal area and then relax those same muscles. This test provides an objective measure of muscle tone and strength. In addition, it can determine whether the nerves in the anorectal area are functioning normally. Anorectal manometry does not require any special preparation beforehand. The test typically takes 30 to 45 minutes, and the results are available within 3 to 4 workdays.
Defecography (Video or Magnetic Resonance)
Defecography is available at only a few specialized medical centers and university hospitals. It can help diagnose problems in the pelvic floor or in the anorectal area. It would be appropriate for a patient who has persistent and severe constipation or who has significant straining during evacuation or feelings of incomplete evacuation. In this study, thick barium paste is inserted into the rectum using a special tube. The patient then sits on a specially designed commode, and the patient is asked to evacuate the barium while x-ray pictures are taken. If an x-ray machine is used, the test is called video defecography. Physicians at some academic medical centers now perform this test in the magnetic resonance (MR) suite. The MR scanner, in contrast to a CT scan, does not use any radiation. MR defecography can provide more information about other organs in the pelvic cavity, such as the bladder, uterus, and vagina, than video defecography.
Although many patients find anorectal manometry or defecography a little embarrassing, neither test is uncomfortable. Defecography (video or MR) is excellent for diagnosing problems that may cause significant constipation and straining, such as a large rectocele (bulge in the rectal wall). Anorectal manometry is very safe; no special preparation is required beforehand, and the test typically takes 45 minutes to perform. The results are available within 1 to 2 days.
Recommendations
At the time of initial evaluation of a patient who has symptoms of IBS, the best diagnostic tool is a thorough and thoughtful history and careful physical examination. If the physical exam is normal and there are no warning signs of serious illness in the patient’s history, then most clinicians can accurately and confidently diagnose IBS without routinely performing multiple diagnostic studies and tests. After the initial office visit, I generally ask that the patient have blood drawn for a CBC, a TSH (if constipated or having severe diarrhea), and an ESR (if diarrhea is present), if these tests have not been done recently. If these laboratory tests were recently performed by another health care provider, there is little value in repeating them unless, of course, symptoms have changed or there are warning signs from the history or physical examination. If a patient’s predominant symptom is diarrhea, I also recommend stool studies for fecal leukocytes, routine bacterial cultures, and ova and parasites (O&P). Stool studies are of no value in evaluating people who have constipation.
Flexible sigmoidoscopy may need to be performed for younger patients (those younger than 40 years of age). This can be scheduled shortly after the initial evaluation for those people who have significant pain in the left lower abdomen, those who have rectal pain, and those who have significant diarrhea where there is concern that the patient may have IBD rather than IBS. Alternatively, sigmoidoscopy can be reserved until after the follow-up visit four to six weeks later and ordered only for those who have not improved with treatment.
For patients 50 years of age and older, the same laboratory tests (CBC, ESR, TSH) noted above should be planned, if not recently performed. However, given the high prevalence of colorectal cancer in the United States, a full colonoscopy should be performed on all patients in this age group. Several research studies have shown that routinely performing abdominal ultrasounds, upper endoscopies, breath hydrogen tests, or CT scans in all people who have IBS does not improve the diagnosis of patients who have IBS, nor does it improve their treatment. Other research studies have shown that when a clinician performs a thorough history and physical examination, and no warning signs are present, the diagnosis of IBS can accurately be made 95 percent to 97 percent of the time. In a long-range study, the diagnosis remained correct even 30 years later. Of course, if new symptoms develop, if warning signs appear, or if reasonable treatment does not improve the symptoms, then specialized testing may be required. For this reason, regular and routine office visits with a primary care physician are helpful and important.
Summary
• Most patients who have IBS can be safely and confidently diagnosed using standardized criteria (the Rome criteria) along with a careful and thorough patient history and physical examination. Many tests are not usually necessary.
• Because many of the symptoms of IBS are not specific to a single disease, many physicians routinely seek only basic laboratory tests (CBC, TSH, ESR) to ensure that an infectious or inflammatory process is not present.
• Stool studies are commonly ordered for patients who have IBS symptoms and diarrhea; they are of little or no value for people who have constipation.
• Specialized testing may prove useful in some patients who have IBS who have persistent symptoms despite dietary interventions and medical therapy. Which tests are appropriate will depend on the symptoms being manifested and their severity. These tests might include anorectal manometry and defecography (for patients with constipation).
• Colonoscopy should be performed in everyone over the age of 50 (and starting at age 45 for African Americans).