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]
Overview
Kidney plays an important role in regulation of serum concentration of sodium, potassium, calcium, phosphate, bicarbonate and chloride as well as levels of hemoglobin, hematocrit, blood pressure and extracellular volume. Hence, chronic injury to the kidney can lead to derangement in the normal values of above mentioned parameters.
Urinalysis
- Albuminuria
- Urine sodium excretion (FENa):
- More useful for Acute renal failure to distinguish prerenal state from acute tubular necrosis (ATN)
- May not be low in volume depleted chronic renal failure patients due to tubular dysfunction
- Hematuria
- Pyuria
- Red cell or white cell casts and crystals
- Urine creatinine levels
- Albumin : Creatinine ratio is used to determine albumin excretion per day.
Fluid and Electrolyte disturbances
- Hypervolemia
- Hyponatremia
- Hyperkalemia
- Hyperphosphatemia
- Hyperchloremia
- Metabolic acidosis
- Most often is mild, pH is rarely below 7.35
- Hypocalcemia
Endocrine and Metabolic disturbances
- Hyperuricemia
- Hypertriglyceridemia
- Decreased HDL levels
- Vitamin D deficiency
- Increased Parathyroid hormone levels
Hematologic abnormalities
Measurement of Renal Function
- Serum creatinine (Cr)
- Determined by glomerular filtration rate (GFR) and by generation, tubular secretion and extrarenal clearance of creatinine
- May be inaccurate estimate of function, particularly in patients with mild renal insufficiency
- Drugs may inhibit tubular secretion of creatinine and falsely elevated serum creatinine (cimetidine, trimethoprim (TMP))
- Creatinine clearance
- Estimate: [(140-age) x body wt (kg)] / [Plasma creatinine x 72] (multiply result x 0.85 for women)
- Calculated based on 24-hour urine collection
- Creatinine clearance (mL/min) = [Urine Creatinine (mg/dL) x Urine volume (mL/d)] / [Plasma Creatinine x 1440]
- If GFR < 50, Creatinine clearance overestimates GFR
- Calculate 24-hour blood urea nitrogen (BUN) clearance (underestimates GFR)
- Average of BUN and Creatinine clearances = GFR
Determination of Chronicity
- Prior creatinine measurements if available
- Acute Renal Failure (ARF) associated with:
- Precipitating factor (nephrotoxin, volume depletion, Urinary tract obstruction)
- More symptoms at given level of Creatinine
- Lesser degree of anemia, hypocalcemia, hyperphosphatemia
- Chronic renal failure associated with:
- Greater likelihood of hematologic and biochemical abnormalities
- Bilateral small kidneys on ultrasound (though can be normal in chronic disease)