A complete evaluation of patients with signs or symptoms of disease usually requires a thorough history and physical examination, as well as efficient diagnostic testing. The correct use of diagnostic testing can confirm or eliminate the presence of disease and improve the cost efficiency of screening tests in a community of people without signs or symptoms of disease. Finally, appropriate and thoughtfully timed use of diagnostic testing allows monitoring of disease and treatment.
Furthermore, health care economics demands that laboratory and diagnostic testing be performed accurately and in a timely fashion. Tests should not have to be repeated because of improper patient preparation, test procedures, or specimen collection technique. The following guidelines will describe the responsibilities of health care providers to ensure safety and accuracy in diagnostic testing.
Patient education is the single most important factor in ensuring accuracy and success of test results. All phases (before, during, and after) of the testing process must be thoroughly explained to the patient. A complete understanding of these factors is essential to the development of nursing processes and standards of care for diagnostic testing.
The interpretation of diagnostic testing is no longer left to the physician alone. In today's complex environment of high-tech testing and economic restrictions, individuals representing many health care professions must be able to interpret diagnostic tests to develop a timely and effective treatment plan.
The International Classification of Diseases, Clinical Modification (ICD-CM) is used to code and classify disease (morbidity data). The ICD-Procedure Coding System (PCS) is used to code inpatient procedures. “ICD-10” is the abbreviated way to refer to 10th revision of these codes. In October 2014, use of ICD-10 will be mandated as a HIPAA requirement. These codes provide an alphanumeric designation for diagnoses and inpatient procedures. These codes are developed, monitored, and copyrighted by the World Health Organization. In the United States, the NCHS (National Center for Health Statistics) which is part of CMS (Centers for Medicare and Medicaid Services) oversees the ICD codes. Using these codes, government health authorities can track diseases and causes of death, and compare mortality. All of the patient's diseases and conditions are converted to an ICD code.
This information is required for use by third-party health care payers and providers and all points of service. Each diagnostic test must reflect the ICD code that most accurately identifies the patient's medical condition. Accurate coding is necessary so that data can be accurately collected, testing accurately interpreted, and medical care properly reimbursed. Complying with this coding requirement is no small task because there are there are about 140,000 codes in the ICD-10 catalogs. See p. xi for a listing of common codes. For additional information about this coding requirement, see http://www.cdc.gov/nchs/icd/icd10.htm; http://www.cms.gov/Medicare/Coding/ICD10/downloads/ICD10FAQs.pdf.
To understand laboratory diagnostic testing, it is helpful to have a basic understanding of commonly performed laboratory methods that can be used on blood, urine, spinal fluid, and other bodily specimens. Most laboratory diagnostic tests use serologic and immunologic reactions between an antibody and an antigen. Precipitation is a visible expression of the aggregation of soluble antigens. Agglutination is a visible expression of the aggregation of particulate antigens or antibodies. As the specimen is progressively diluted, persistent precipitation or agglutination indicates greater concentrations of the antigen or antibody. Dilution techniques are therefore used to quantify the pathologic antigen or antibody in the specimen. Commonly used laboratory methods and their variations are described in the following.
Latex agglutination is a common laboratory method in which latex beads (that become visibly obvious when agglutination occurs) are coated with antibody molecules. When mixed with the patient's specimen containing a particular antigen, agglutination will be visibly obvious. C-reactive proteins are identified by this method. In an alternative latex agglutination method (for example, as needed for pregnancy testing or rubella testing), latex beads are coated with a specific antigen. In the presence of antibodies in the patient's specimen to that specific antigen on the latex particles, visible agglutination occurs.
Agglutination inhibition is another laboratory method based on the agglutination process. In this process, if one is trying to identify a particular molecule, for example hCG, the patient's specimen is incubated with anti-hCG. Latex particles coated with hCG are then added to the mixture. If the patient’s specimen contains hCG, those molecules will attach to the anti-hCG during incubation leaving no anti-hCG molecules to attach to the hCG coated latex beads. Therefore, agglutination would not occur because the patient’s endogenous hCG “inhibited” the agglutination.
Hemagglutination laboratory methods are used to identify antibodies to antigens on the cell surface of red blood cells (RBCs). Like latex, RBC agglutination is visible. Blood typing for transfusions uses this laboratory method. In an alternate method of hemagglutination, different antigens can be bound to the RBC surface. When added to the patient's specimen, specific antibodies can be identified by RBC agglutination.
Electrophoresis is an analytic laboratory method where an electrical charge is applied to a medium on which the patient's specimen has been placed. Migration of charged molecules (particularly proteins) in the specimen can be separated in an electrical field. Proteins can then be identified based on their rate of migration. Serum protein electrophoresis utilizes this method.
Immunoelectrophoresis is a laboratory method that allows the previously electrophoresed proteins to act as antigens to which known specific antibodies are added. This provides specific protein identification. With dilution techniques as described, these particular proteins can be quantified. This method is used to identify gammopathies, hemoglobinopathies, and Bence Jones proteins.
Immunofixation electrophoresis (IFE) is particularly helpful in the identification of certain diseases. In this method, a specific known antibody is added to a previously electrophoresed specimen. The antigen/antibody complexes become fixed (that is attached) to the electrophoretic gel medium. When the non-fixed proteins are washed away, the protein immune complexes that remain fixed to the gel are stained with a protein-sensitive stain and can be identified and quantified. IFE is particularly helpful in identifying proteins that exist in very small quantities in the serum, urine, or CSF.
Immunoassay is an important laboratory method of diagnosing disease. In the past, radioimmunoassay (RIA) was performed using a radioactive label that could identify an antibody/antigen complex at very low concentrations. Unfortunately, there are significant drawbacks of using radioactive isotopes as labels. Radioactive labels have a short half-life and are hard to keep on the shelf. These labels require considerable care to avoid environmental exposure. And finally, the costs associated with disposal of radioactive waste are high.
Enzyme linked immunosorbent assay (ELISA) techniques are able to detect immunocomplexes more easily when compared to RIA. This ELISA technique (also known as enzyme immunoassay [EIA]) is able to detect antigens or antibodies by producing an enzyme-triggered color change. In this method, an enzyme-labeled antibody or antigen is used in the immunologic assay to detect either suspected abnormal antibodies or antigens in the patient's specimen. In this method, a plastic bead (or a plastic test plate) is coated with an antigen (e.g., virus). The antigen is incubated with the patient’s serum. If the patient’s serum contains antibodies to the pathologic viral antigen, an immunocomplex forms on the bead (or plate). When a chromogenic chemical is then added, a color change is noted and can be spectrophotometrically compared with a control (or reference) serum identification. Then, quantification of abnormal antibodies in the patient’s serum instigated by the viral infection can be performed. Similarly EIA can also be used for detection of pathologic antigens in the patient’s serum. Testing for HIV, hepatitis, or cytomegalovirus commonly uses these methods.
Autoimmune enzyme immunoassay screening tests are commonly used for the detection of antinuclear antibodies. EIA techniques (similar to what have been described in the preceding) are used as the purified nuclear antigens are bound to a series of microwells to which the patient's serum is serially diluted and added. After adding up peroxidase conjugated antihuman IgG, a complex antibody/antigen “sandwich” is identified by color changes.
Chemiluminescent immunoassays are extensively used in automated immunoassays. In this technique, chemiluminescent labels can be attached to an antibody or antigen. After appropriate immunoassays are obtained (as described), light emission produced by the immunologic reaction can be measured and quantified. This technique is commonly used to detect proteins, viruses, and nucleic acid sequences associated with disease.
Fluorescent immunoassays consist of labeling antibody with fluorescein. This fluorescein-labeled antibody is able to bind either directly with a particular antigen or indirectly with antiimmunoglobulins. Under a fluorescent microscope, the fluorescein becomes obvious as yellow-green light. Testing for Neisseria gonorrhea or antinuclear antibodies may use these laboratory methods.
With the increasing use of automated analyzers, the use of chemiluminescence and nephelometry has become extremely important to allow analyzers to quantify results in great numbers of specimens tested in a short period of time. Nephelometry (in auto analyzers) depends on the light-scattering properties of antigen/antibody complexes as light is passed through the test medium. The quantity of the cloudiness or turbidity in a solution then can be measured photometrically. Automated C-reactive protein, alpha antitrypsin, haptoglobins, and immunoglobulins are often measured using nephelometry.
Since the complete human genome sequence became available in 2003, laboratory molecular genetics has become an integral part of diagnostic testing. Molecular genetics depends on an in vitro method of amplifying low levels of specific DNA sequences in a patient specimen to raise quantities of a potentially present specific DNA sequence to levels that can be quantitated by further analysis. This process is called Polymerase Chain Reaction (PCR). This is particularly helpful in the identification of diseases caused by gene mutations (e.g., BRCA mutations), in the identification and quantitation of infectious agents such as HPV or HIV, and in the identification of acquired genetic changes that may be present in hematologic malignancies or colon cancer.
In PCR procedures, a known particular target short DNA sequence (ranging from 100 to 1000 nucleotide pairs) is used. This known DNA sequence “primer” is then placed in a series of reactions with the patient's specimen. These reactions are designed to markedly increase the number of comparable abnormal DNA sequences that potentially exist in the patient's specimen. The increased number of abnormal DNA sequences then can be identified and quantified. In many instances, the nucleic acid of interest is ribonucleic acid (RNA) rather than DNA. In these circumstances, the PCR procedure is modified by reverse transcription (reverse transcriptase PCR [RT PCR]). With RT PCR, abnormal RNA can be amplified (increased in number), detected, and quantified.
Real-time PCR uses the same reaction sequence as described. In real-time PCR, fluorescence resonance energy transfer is used to quantitate the DNA sequences of interest and identify points of mutation. Real-time PCR provides a product that can be more accurately quantified.
Quantification of PCR derived DNA/RNA products can be performed in many ways. This can be performed by simple gel electrophoresis, DNA sequencing, or using DNA probes. DNA probes are presynthesized DNA primers that are used to identify and quantify the amplified DNA produced by the PCR process. Hybridization techniques such as liquid phase hybridization interact with a defined DNA probe and the potential targeted DNA in solution. DNA probes have become a very important part of commercial laboratory molecular genetics. Microarray DNA chip technology (Microarray analysis) places thousands of major DNA probes on one glass chip. After interaction with the patient’s specimen, the microarray chip can then be scanned with high speed fluorescent detectors that can quantify each DNA micro sequence. This process is used to identify gene expression of malignancies and has led to a new understanding of the classification, pathophysiology, and treatment of cancer.
Fluorescence in situ hybridization (FISH) uses nucleic probes (short sequences of single-stranded DNA) that are complementary to the DNA sequence to be identified. These nucleic probes are labeled with fluorescent tags that can identify the exact location of the complementary DNA sequence that is being targeted. This method is particularly helpful in the detection of inherited and acquired chromosomal abnormalities common in hematologic and other oncologic conditions, such as lymphomas and breast cancer. Laboratory genetics are also discussed on p. 1104.
The risk of spread of diseases such as hepatitis B virus (HBV) and human immunodeficiency virus (HIV) has made all health care organizations aware of the need to protect health care providers. These threats prompted the Centers for Disease Control and Prevention (CDC) to release its guidelines for universal precautions, now called Standard Precautions (Box 1-1). This policy recommends that blood and body fluid precautions be used for all patients regardless of their infection status. All patients should be considered potentially infectious. The Standard Precautions apply to all blood, body fluids, and tissues. Serous fluids such as pleural, peritoneal, amniotic, cerebrospinal, and synovial fluids are included. Semen and vaginal secretions should also be considered hazardous. Other clinical specimens (e.g., sputum, stool, urine) are of less concern, and the Standard Precautions apply only if these specimens contain visible amounts of blood.
These precautions require the use of protective barriers (gloves, gowns, masks, protective eyewear) to avoid skin and mucous membrane exposure to blood and body fluids. A fundamental principle of Standard Precautions is frequent handwashing between patients and when gloves are changed. All specimens should be collected and transported in containers that prevent leakage. Blood or body fluid spills must be decontaminated immediately. All needles and other sharp items must be handled carefully and discarded in puncture-resistant containers. Needles should not be recapped, broken, bent, or removed from a syringe to avoid the risk of puncturing the finger or hand. All needle sticks need to be reported and followed up with appropriate testing for infectious disease. Special reusable needles are placed in metal containers for transport to a designated area for sterilization or disinfection.
Vaccination against HBV is another safety precaution recommended by the CDC.
Because of the cost and complexity of laboratory and diagnostic testing, it is important that tests be scheduled in the most efficient sequential manner. Because one type of test can interfere with another, certain guidelines apply when multiple tests must be performed in a limited amount of time. X-ray examinations that do not require contrast material should precede examinations that do require contrast media. X-ray studies using barium should be scheduled after ultrasonography studies. For example, x-ray studies using barium should follow x-rays using iodine contrast dye (such as intravenous pyelography [IVP]), which should follow x-ray studies using no contrast because contrast agents can obscure visualization of other body areas on subsequent x-ray tests. Also, stool specimens should be collected before x-ray studies using barium.
Test sequencing affects the ability to efficiently perform tests in a limited time period. An essential component of this process is communication and collaboration with other health care workers in numerous departments.
Patient preparation is vital to the success of any diagnostic test. Patient education is essential and is discussed later in this chapter. Development of and adherence to patient care guidelines in regard to patient preparation for the test require an understanding of the procedure. A thorough history to identify contraindications to the specific test is vital. Recognizing patients at risk for potential complications and counseling them about those complications is important. The fears and concerns of the patient should be elicited and addressed prior to testing. Documentation and a thorough understanding of ongoing factors (e.g., medications, previous tests, other variables as discussed later in this chapter) that could interfere with the test results are essential to avoid misinterpretation of diagnostic testing.
Pretest preparation procedures must be followed closely. Dietary restriction is often an important factor in preparing the patient for tests. Studies requiring fasting should be performed as early in the morning as possible to diminish patient discomfort. Adherence to dietary restriction is important for test accuracy. Many blood tests and procedures require fasting. Studies such as a barium enema, colonoscopy, upper gastrointestinal (GI) series, and IVP are more accurate if the patient has been on NPO (nothing by mouth) status for several hours before the test. Sometimes dietary restrictions are important for safety, especially if a sedative is to be administered during testing. For example, upper GI endoscopy requires that the patient remain NPO for 8 to 12 hours before the test to prevent gagging, vomiting, and aspiration. Bowel preparation is necessary for many procedures designed to evaluate the mucosa of the GI tract.
Equally important to total patient care is the coordination of ongoing therapy (e.g., physical therapy, administration of medications, other diagnostic testing). Finally, correct timing of testing is key to accurate interpretation of results. For example, blood samples for cortisol, parathormone, and fasting glucose levels (among others) must be obtained in the early morning hours.
Proper identification of the patient is a critical safety factor. The conscious patient should be asked to state his or her full name. The name should be verified by checking the identification band and requisition slip. The identity of an unconscious patient should be verified by family or friends. No specimens should be collected or procedure performed without properly identifying the patient. Costly tests on the wrong patient are useless and may instigate legal action. Confusion can occur when patients with the same name are on the same nursing unit. Most units have some type of warning or “name alert” to address this concern.
Once the patient is properly identified and the proper test or procedure is scheduled, patient education begins. Patients want to know what tests they are having and why they are needed. An informed patient is less apprehensive and more cooperative. Patient education helps ensure that the test will not need to be repeated because of improper preparation. Fasting requirements and bowel preparations must be clearly explained to the patient. Written instructions are essential. If used, the patient's literacy and understanding of the material should be validated. Sometimes medications need to be discontinued for a period of time before certain tests. This information should be determined in consultation with the physician. Medications that are not discontinued may be listed on the requisition to aid in interpretation of test results. Finally it is extremely important to inform the patient regarding the need to discontinue medications or foods that may interfere with testing results.
Many laboratory tests are affected by individual variables that must be considered in test result interpretation. Several of these key variables are discussed in the following paragraphs.
Pediatric reference values differ from adult values. For some tests, values vary according to the week of life of the infant. For example, in the first week of life, newborns have elevated levels of serum bilirubin, growth hormone, blood urea nitrogen (BUN), and fetal hemoglobin. They have decreased levels of cholesterol and haptoglobin. Healthy newborns also have an increase in total white blood cells and decreases in immunoglobulin (Ig) M and IgA. For some tests, children have different reference values based on their developmental stage. For example, alkaline phosphatase levels in children are much higher than adult values because of rapid bone growth.
Age-related changes are also apparent in the middle adult and older adult years. For example, albumin and total protein levels begin to decline in the mid-adult years. Reference values for cholesterol and triglyceride levels begin to increase in the mid-adult years. Creatinine clearance levels decrease with age relative to changes in glomerular filtration rate.
Gender is another variable that affects values in men and women. Differences are usually related to increased muscle mass in men and differences in hormonal secretion. For example, men usually have higher reference values for hemoglobin, BUN, serum creatinine, and uric acid. Men also have higher serum levels of cholesterol and triglycerides as compared with premenopausal women. Sex-specific hormones will also differ, with men having higher testosterone levels and women having higher levels of estrogens, follicle-stimulating hormone, and luteinizing hormones.
Generally race has little effect on laboratory values. It has a greater effect on genetic diseases, such as sickle cell anemia in blacks and thalassemia in individuals with origins near the Mediterranean Sea.
Many endocrine, hematologic, and biochemical changes occur during pregnancy. Pregnant women have increased levels of cholesterol, triglycerides, lactic dehydrogenase, alkaline phosphatase, and aspartate aminotransferase. They may have lower values of hemoglobin, hematocrit, serum creatinine, urea, glucose, albumin, and total protein.
Several serum values are markedly affected by food. For example, levels of glucose and triglycerides rise after a meal. To avoid the effects of diet on laboratory tests, many tests are obtained when the patient is in the fasting state.
Changes in body position affect the concentration of several components in the peripheral blood. Therefore it is sometimes important to note whether the patient was in the supine, sitting, or standing position when blood was drawn. Examples of laboratory values affected by posture include norepinephrine, epinephrine, renin, aldosterone, protein, and potassium.
Often many different health care professionals are needed to successfully perform a diagnostic procedure. The health care provider's knowledge of the procedure will be a major determinant of the success of the procedure. Furthermore, the presence of a knowledgeable and supportive health care provider during any procedure is invaluable to the patient and to the accuracy of the test.
Protocols and guidelines are available for each type of specimen collection. These are essential for appropriate preparation and collection. For example, the selection of the color-coded tube varies with the type of blood test needed. Guidelines for the collection of a 24-hour urine collection must be followed to obtain a representative urine sample. These and other examples are described in detail in the following chapter overviews.
Preparing the patient and collecting the specimen are essential. Getting the specimen to the laboratory in an acceptable state for examination is just as important. In general, the specimen should be transported to the laboratory as soon as possible after collection. Delays may result in rejection of the specimen. Specimens are usually refrigerated if transportation is delayed.
The International System of Units (SI units) is a system for reporting laboratory values in terms of standardized international measures. This system is currently used in many countries, and it is expected to be adopted worldwide. Throughout this book results are given in conventional units and SI units when possible.
Posttest care is an important aspect of total patient care. Attention should be directed to the patient's concerns about possible results or the difficulties of the procedure. Appropriate treatment subsequent to testing must be provided. For example, after a barium test, a cathartic is indicated. However, if a bowel obstruction has been identified, catharsis is contraindicated.
Recognition and rapid institution of treatment of complications (e.g., bleeding, shock, bowel perforation) is essential in caring for the patient who has just had a diagnostic procedure. More invasive tests often require heavy sedation or a surgical procedure. In these situations, aftercare is similar to routine postoperative care.
Although proper patient preparation and skill and accuracy in performing test procedures are vital, timeliness in reporting test results is no less essential. To be clinically useful, results must be reported promptly. Delays in reporting test results can make the data useless. The data must be included in the appropriate medical record and presented in a manner that is clear and easily interpreted. As in all phases of testing, communication among health care professionals is important. Health care providers need to understand the significance of test results. For example, nurses on the evening shift may be the first to see the results of a culture and sensitivity report on a patient with a urinary tract infection. If the results indicate that the infecting organism is not sensitive to the prescribed antibiotic, the doctor should be informed and an appropriate antibiotic order obtained.
Ethical standards for disclosure of test results must be strictly followed. In 1996, the Health Insurance Portability and Accountability Act (HIPAA) became law. Its purpose was to improve the health care of each individual by insuring the ability for each person to obtain reasonable health care, and to allow each individual access to and protection of his or her health care information. In response to the HIPAA mandate, Health and Human Services published the Standards for Privacy of Individually Identifiable Health Information (the Privacy Rule) in December 2000, which became effective on April 14, 2001. The Privacy Rule set national standards for the protection of an individual's health information. Compliance with this rule is particularly important when providing diagnostic test results. The Privacy Rule generally gives patients the right to examine and obtain a copy of their own health records and to request corrections. It limits who can have access to results of diagnostic tests. Information regarding test results can only be provided to the patient and to persons the patient indicates (by signature). Only health care workers who have a provider relationship with a patient may obtain access to a patient's test results. The federal government has responsibility for enforcing these laws and violators are subject to civil and criminal prosecution. Fines can be levied against both the individual and the health organization. The penalties for violation of these laws are fines up to $250,000 and up to 10 years in jail.
As a result of the Privacy Rule, test results are not given over the phone to patients. Results, no matter if normal or not, are never left on “answering machines.” Results cannot be given to family or friends unless written consent is provided. These restrictions include providing test results to spouses, parents of adult children, siblings, or children. If the patient presents in the laboratory or a clinical area, the patient is usually required to show a photo identification to confirm his or her identity and to verify his or her signature on a Release of Information Authorization form. The Privacy Rule does not negate state regulations that affect test result reporting. For example, in most states, HIV results are released only to the ordering physician/provider and are not provided by the laboratory to the patient. Compliance with the Privacy Rule is an extremely important part of diagnostic testing and patient education. The impact of an abnormal test result on the patient must always be appreciated, and support must be provided.
Knowledge of the implications of various test results and an understanding of the disease process are as important as the communicative skills required to inform the patient and the family. Succinct documentation of test results may be required before the “official” result is included in the patient's chart. Again, a thorough understanding of the test is essential. Adequate follow-up is as important as all previously mentioned factors for successful diagnostic testing. The patient must be educated about home care, the next doctor's visit, and treatment options.
Knowledgeable interpretation of diagnostic tests is key for effective collaboration among health care providers if the most efficient patient care is to be provided. The safety and success of diagnostic testing often depend on the nurse and other health care professionals. The safety of the patient and health care professionals depends on the creation of practice guidelines and standards of care. These can be effectively developed only with a thorough understanding of laboratory and diagnostic testing.