Laboratory Values

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Answering questions about lab values is another example of how the real world does not work on the NCLEX-PN^® exam. In practical/vocational nursing school, you learned lab values for specific tests and you may not have remembered them after the test. While you were in the clinical setting, the emphasis was on interpretation of lab values. Because most lab slips contained a listing of normal values, you were able to compare the client’s results to the normal levels. Questions on the NCLEX-PN^® exam will not provide you with a listing of normal lab values.

To answer questions on the NCLEX-PN^® exam, you must:

• Know normal lab test results.
• Correctly interpret normal or abnormal lab test results.

Compare the following two questions.

1. A client is admitted to the hospital with flu-like symptoms. When taking the history, the LPN/LVN learns that the client has been taking digoxin 0.125 mg PO daily and furosemide 40 mg PO daily for 3 years. Last month her physician changed the prescription for digoxin to 0.25 mg qd. The LPN/LVN would expect the physician to order which of the following laboratory tests?
   1. Serum electrolytes and digoxin level
   2. White blood cell count, hemoglobin, and hematocrit
   3. Cardiac enzymes and an arterial blood gas
   4. Blood cultures and urinalysis

Most of you are probably familiar with the concepts presented in this question. The physician has increased the client’s dose of digoxin. Furosemide (Lasix) is a loop diuretic that inhibits resorption of sodium and chloride; side effects include hypotension, hypokalemia, GI upset, and weakness. Hypokalemia may increase the client’s risk of digitalis toxicity. Serum electrolytes and digoxin level (1) is the correct answer.

Now look at this question.

1. The LPN/LVN implements care for a teenager admitted with fever, vomiting, and diarrhea. The LPN/LVN sees the following nursing diagnosis on the client’s care plan: “fluid volume deficit.” Which of the following changes in laboratory values would demonstrate an improvement in the client’s condition?
   1. Urine specific gravity, 1.015; hematocrit, 37%
   2. Urine specific gravity, 1.020; hematocrit, 45%
   3. Urine specific gravity, 1.032; hematocrit, 52%
   4. Urine specific gravity, 1.025; hematocrit, 35%

In order to correctly answer this question, you must know:

• The specific gravity of urine (1.010–1.030) and the normal levels of hematocrit (male 42–50%, female 40–48%)
• How the hematocrit and specific gravity levels are affected by a fluid volume deficit

Fluid volume deficit occurs when water and electrolytes are lost in the same proportion as they exist in the body. When a client is dehydrated, both the specific gravity of urine and the hematocrit become elevated. The correct answer is (2).

Answer this question:

1. A client is hospitalized with a diagnosis of atrial fibrillation. Heparin 5,000 units is ordered every 12 hours to be given subcutaneously. The health care provider orders daily partial thromboplastin times (PTTs). The result of the client’s most recent PTT is 55 seconds. Which of the following actions should be taken by the LPN/LVN?
   1. Document the results and administer the heparin.
   2. Withhold the heparin.
   3. Notify the health care provider.
   4. Have the test repeated.

In order to answer this question you need to know:

• The normal range for a PTT is 20–45 seconds.
• The therapeutic range for a client receiving heparin, an anticoagulant, is 1.5–2 times the control or normal level.
• To calculate the therapeutic range, take the lower number for the normal range for a PTT (20) and multiply it by 1.5. The result is 30. Multiply the higher number (45) by 2. The result is 90. Thus the therapeutic range goes from 30 to 90. Any result that falls within 30 to 90 seconds is considered therapeutic. The goal is to keep the PTT within this range.

Evaluate the answer choices:

1. “Document the results and administer the heparin.” The client’s most recent PTT is 55. This is within the therapeutic range of 30 to 90, so the nurse should administer the medication.
   
2. “Withhold the heparin.” A side effect of heparin is bleeding. If the clotting time is greater than 90 seconds, the nurse should notify the health care provider.
3. “Notify the health care provider.” There is no reason to notify the health care provider, since the PTT is within the therapeutic range.
4. Have the test repeated. There is no reason to have the test repeated. 

The correct answer is (1).