Chronic renal failure laboratory tests

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]

Chronic kidney disease is defined as the presence of markers of kidney damage for > 3 months, and may include abnormalities in markers in blood or urine, and imaging test and/or GFR < 60 mL/min/1.73 m2 for > 3 months with or without other signs of kidney damage. The kidneys play an important role in the regulation of serum concentration of electrolytes such as sodium, potassium, calcium, phosphate, bicarbonate and chloride as well as levels of hemoglobin, hematocrit, blood pressure and extracellular volume. Hence, chronic injury to the kidneys can lead to derangement in the normal values of above mentioned parameters.

• Albuminuria
  • Normal levels of urine protein, albumin are:
    • 24 hour protein excretion = Normal < 150 mg, nephrotic range of protein excretion > 3.5 gram
    • Albumin/creatinine = Normal < 30 mg, microalbuminuria = 30-300 mg, macroalbuminuria > 300 mg
    • Protein/creatinine = Normal < 200 mg/g, Proteinuria > 200 mg/g
• Urine sodium excretion (Fractional excretion of sodium):

  • More useful for Acute renal failure to distinguish prerenal state from acute tubular necrosis (ATN)
  • May not be low in volume depleted CRF patients due to tubular dysfunction

• Hematuria
• Pyuria
• Red cell or white cell casts and crystals
• Urine creatinine levels

• Hypervolemia
• Hyponatremia
• Hyperkalemia
• Hyperphosphatemia
• Hyperchloremia
• Metabolic acidosis

  • Most often is mild, pH is rarely below 7.35

• Hypocalcemia

• Hyperuricemia
• Hypertriglyceridemia
• Decreased HDL levels
• Vitamin D deficiency
• Increased Parathyroid hormone levels

• Normocytic normochromic anemia
• Lymphocytopenia
• Leukopenia
• Thrombocytopenia

Chronic Kidney Disease is defined as:

• Presence of markers of kidney damage for > 3 months, and may include abnormalities in markers in blood or urine, and imaging tests.
• GFR < 60 mL/min/1.73 m2 for > 3 months with or without other signs of kidney damage.

The stages of CKD is based on the GFR and other renal function abnormalities. The different stages of chronic kidney diseases are as follow:

• Stage 1: GFR>90 ml/min/1.73m2 and evidence of kidney damage

• Stage 2: GFR 60-89 ml/min/1.73m2 and evidence of kidney damage

• Stage 3: GFR 30-59 ml/min/1.73m2

• Stage 4: GFR 15-29 ml/min/1.73m2

• Stage 5: GFR <15 ml/min/1.73m2

Using serum creatinine alone as an indicator of kidney function may be misleading. This is because the calculated creatinine levels depends on age, gender, race, nutritional status and muscle mass. At GFR levels ≥60 ml/min/1.73 m2, neither the Cockroft and Gault equation nor the MDRD equation provides a reliable measurement of kidney function. The CKD-EPI equation is more accurate than the Cockcroft and Gault equation and the MDRD equation at GFR levels ≥60 ml/min/1.73 m2.

• Serum creatinine (Cr)

  • Determined by glomerular filtration rate (GFR) and by generation, tubular secretion and extrarenal clearance of creatinine
  • May be an inaccurate estimate of renal function, particularly in patients with mild renal insufficiency
  • Drugs may inhibit tubular secretion of creatinine and falsely report elevated serum creatinine (cimetidine, trimethoprim)

• 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

Cystatin C allows a more precise testing of kidney function than creatinine.^[1]

Measurement of urinary neutrophil gelatinase-associated lipocalin (NGAL) can help distinguish chronic kidney disease from acute kidney injury.^[2]

• Prior creatinine measurements if available
• Acute Renal Failure (ARF) is associated with:

  • Precipitating factor (nephrotoxin, volume depletion, urinary tract obstruction)
  • More symptoms at given bodily levels of creatinine
  • Lesser degree of anemia, hypocalcemia, hyperphosphatemia

• Chronic renal failure is associated with:

  • Greater likelihood of hematologic and biochemical abnormalities
  • Bilateral small kidneys on ultrasound (though can be normal in chronic disease)

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