Chronic renal failure laboratory tests
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]
Screening / Diagnostic Laboratory Studies
Measurement of Renal Function
- Serum creatinine (Cr)
- Determined by glomerular filtration rate (GFR) and by generation, tubular secretion and extrarenal clearance of Cr
- May be inaccurate estimate of function, particularly in patients with mild renal insufficiency
- Drugs may inhibit tubular secretion of Cr and falsely elevated serum Cr (cimetidine, trimethoprim (TMP))
- Creatinine clearance
- Estimate: [(140-age) x body wt (kg)] / [Plasma Cr x 72] (multiply result x 0.85 for women)
- Calculated based on 24-hour urine collection
- CrCl (mL/min) = [Urine Cr (mg/dL) x Urine volume (mL/d)] / [Plasma Cr x 1440]
- If GFR < 50, CrCl overestimates GFR
- Calculate 24-hour blood urea nitrogen (BUN) clearance (underestimates GFR)
- Average of BUN and Cr clearances = GFR
Determination of Chronicity
- Prior Cr measurements if available
- Acute Renal Failure (ARF) associated with:
- Precipitating factor (nephrotoxin, volume depletion, obstruction)
- More symptoms at given level of Cr
- Lesser degree of anemia, hypocalcemia, hyperphosphatemia
- CRI associated with:
- Greater likelihood of hematologic and biochemical abnormalities
- Bilateral small kidneys on ultrasound (though can be normal in chronic disease)
Urinalysis
- May suggest glomerular vs. nonglomerular cause
- Urine sodium excretion (FENa):
- More useful for ARF to distinguish prerenal state from acute tubular necrosis (ATN)
- May not be low in volume depleted CRI patient due to tubular dysfunction