Laboratory Values

---

Answering questions about laboratory values is another example of how the real world does not work on the NCLEX-PN^® exam. In practical/vocational nursing school, you learned laboratory 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 laboratory values. Because most lab slips contained a listing of normal values, you were able to compare the client’s results to the normal values. Questions on the NCLEX-PN^® exam will not provide you with a listing of normal laboratory values.

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

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

Compare the following two questions.

1. A client is admitted to the hospital with influenza-like symptoms. When taking the client's history, the LPN/LVN learns that the client had been taking digoxin 0.125 mg PO daily and furosemide 40 mg PO daily for 3 years. Last month the primary health care provider changed the prescription for digoxin to 0.25 mg daily. The LPN/LVN would expect the primary health care provider to prescribe which of the following laboratory tests?
   1. Serum electrolyte and digoxin levels.
   2. Hemoglobin level and hematocrit.
   3. Cardiac enzymes and arterial blood gas analysis.
   4. Blood culture and sensitivity and urinalysis.

Most of you are probably familiar with the concepts presented in this question. The primary health care provider has increased the client’s digoxin dose. Furosemide 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 is caring for a client 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 test results would demonstrate an improvement in the client’s condition?
   1. Urine specific gravity, 1.015; hematocrit, 37% (0.37).
   2. Urine specific gravity, 1.020; hematocrit, 45% (0.45).
   3. Urine specific gravity, 1.032; hematocrit, 52% (0.52).
   4. Urine specific gravity, 1.025; hematocrit, 35%  (0.35).

To correctly answer this question, you must know:

• Normal urine specific gravity ranges 1.010–1.030 and normal hematocrit ranges  42–50% (0.42–0.50) for a male,  40–48% (0.40–0.48) for a female
• How fluid volume deficit affects hematocrit and specific gravity

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

Answer this question:

1. A client is hospitalized with a diagnosis of atrial fibrillation. The primary health care provider prescribes heparin 5,000 units every 12 hours to be given by subcutaneous injection and a daily partial thromboplastin time (PTT). 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 primary health care provider of the test results.
   4. Have the test repeated.

To answer this question you need to know:

• Normal PTT ranges 20–45 seconds.
• Therapeutic range PTT for a client receiving heparin, an anticoagulant, ranges 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 ranges from 30 to 90 seconds. Therapeutic PTT ranges 30 to 90 seconds, the goal of therapy. 

Evaluate the answer choices:

1. “Document the results and administer the heparin.” The client’s most recent PTT is 55 seconds. This falls within the therapeutic range of 30 to 90 seconds, so the LPN/LVN should administer the medication.
   
2. “Withhold the heparin.” A side effect of heparin is bleeding, which can occur when PTT rises above therapeutic range. If the PTT measures greater than 90 seconds, the nurse should notify the primary health care provider.
3. “Notify the primary health care provider of the test results.” There is no reason to notify the primary health care provider, since the PTT falls within the therapeutic range.
4. “Have the test repeated.” There is no reason to have the test repeated, since it falls within normal range. 

The correct answer is (1).