Acute tubular necrosis laboratory findings
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CBC, urinalysis with sediment microscopy, urine electrolytes, osmolarity, serum electrolytes, blood urea nitrogen and serum creatinine, and urine dipstick are commonly performed in patients to evaluate acute tubular necrosis and other causes of acute renal failure. Urine sediment may show tubular epithelial cells and epithelial cell casts or brown muddy granular casts. Increased urine sodium concentration >40 mEq/L, urine fractional excretion of sodium greater than 2 percent along with elevated serum creatinine concentration at a rate greater than 0.3 mg/dL/day may be found in acute tubular necrosis. However, these tests may have some limitations.
- Complete blood count (CBC):
- Urine sediment microscopy may show muddy brown granular casts from necrotic tubular cells binds with tamm horsfall protein or epithelial cell casts, and renal tubular epithelial cells. Acute tubular necrosis caused by rhabdomyolysis and hemolysis, urinalysis may show heme-positive urine with out erythrocytes.
- Urine sodium concentration: Urine sodium concentration is high >40 mEq/L
- Urine fractional excretion of sodium concentration: > 2%
- Urine osmolarity: <350 mosmol/kg
- Serum electrolyte abnormalities: Hyperkalemia, hyperphosphatemia, hyponatremia, hypocalcemia, and hypomagnesemia may be found.
- Urine/plasma creatinine ratio: <20
- Fractional excretion of urea: >35%
- Urine/plasma urea nitrogen:<3
- Ratio of BUN/sr.creatinine: 10 to 15:1 and is normal.
- Rate of creatinine concentration in serum rise: Serum creatinine levels are increased progressively at a rate greater than 0.3 to 0.5 mg/dL/day.
- Specific gravity: Low <1.020
- Urine dipstick test: Commonly performed for blood pigments, proteins, WBC, nitrites, and glucose in all patients with suspected renal failure to exclude certain etiologies such as infection, hemolysis, myoglobinuria, and rhabdomyolysis.
|Urine sediment microscopy||Muddy brown granular casts and epithelial cell casts|
|Urine sodium||>40 mEq/L|
|Fractional excretion of sodium||> 2%|
|Urine osmolarity||<350 mosmol/kg|
|Urine/plasma creatinine ratio||<20|
|Ratio of BUN/sr.creatinine||10 to 15:1|
|Urine/plasma urea nitrogen||<3|
|Serum electrolytes||Hyperkalemia (↑K)|
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