What is the role of lab studies in the workup of azotemia?

Updated: Apr 24, 2020
  • Author: Moro O Salifu, MD, MPH, FACP; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

For the initial evaluation, obtain a complete blood count (CBC), a biochemical profile, urinalysis, and urine electrolyte concentrations. In addition to establishing the presence of systemic disease, these tests may reveal clues to the origin of the azotemia. Diagnostic indices are commonly used to differentiate prerenal azotemia from intrarenal or postrenal azotemia (see in the image below).

Diagnostic indices in azotemia. Although such indices are helpful, it is not necessary to perform all these tests on every patient. Comparison should always be made with patients' baseline values to identify trends consistent with increase or decrease in effective circulating volume. Use of some of these indices may be limited in certain clinical conditions, such as anemia (hematocrit), hypocalcemia (serum calcium), decreased muscle mass (serum creatinine), liver disease (blood urea nitrogen [BUN], total protein, and albumin), poor nutritional state (BUN, total protein, and albumin), and use of diuretics (urine sodium). Fractional excretion of urea and fractional excretion of trace lithium appear to be superior for assessing prerenal status in patients on diuretics.

Diagnostic indices in azotemia. Although such indi Diagnostic indices in azotemia. Although such indices are helpful, it is not necessary to perform all these tests on every patient. Comparison should always be made with patients' baseline values to identify trends consistent with increase or decrease in effective circulating volume. Use of some of these indices may be limited in certain clinical conditions, such as anemia (hematocrit), hypocalcemia (serum calcium), decreased muscle mass (serum creatinine), liver disease (blood urea nitrogen [BUN], total protein, and albumin), poor nutritional state (BUN, total protein, and albumin), and use of diuretics (urine sodium). Fractional excretion of urea and fractional excretion of trace lithium appear to be superior for assessing prerenal status in patients on diuretics.

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