Acute renal failure: urine tests may help differentiate renal failure causes.

Clinical bottom line (level 4)

  1. In patients with acute renal failure, urinary sodium or chloride <10 mmol/l diagnosed prerenal failure.
  2. A fractional excretion of sodium >1% (LR+0.16) or chloride>1% (LR+0.050) made prerenal failure much less likely.
Anderson et al: Mineral Electrolyte Metabolism 1984; 10: 92-97
Expires July 2003

The study

Setting: three university hospitals, USA

68 patients (aged mean ~50 to 60 years, ~70% male) acute renal failure defined as an increase in serum creatinine from <76 µ mol/l to >123 µ mol/l

Excluded if
  • chronic renal failure
  • received diuretics in the past 24 hours



    • Independent ?blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
    Reference standard:
    • prerenal azotemia defined as:
      • oliguria (<500 ml urine/day
      • development of renal failure in the context of hypovolaemia, congestive heart failure or transient hypotension
      • return of renal function to normal within 72 hours of correction of precipitating factors
      • absence of casts on urinalysis
    Diagnostic test:
    • urine sodium concentration
    • urine chloride concentration
    • fractional excretion of sodium (urine Na x plasma creatinine)/(plasma Na x urine creatinine) x 100
    • fractional excretione of chloride (urine Cl x plasma creatinine)/(plasma Cl x urine creatinine) x 100

    The evidence

    pre-test probability of prerenal failure: 31%, (95% CI: 20% to 42%)

    diagnostic test prerenal failure not prerenal failure LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    urine sodium <10 mmol/l 6 0 inf
    (4.6 to inf)     		100%
    ( to )
    urine sodium 10-20 mmol/l 6 3 4.5
    (1.2 to 16)     		67%
    ( to )
    urine sodium >20 mmol/l 9 44 0.46
    (0.28 to 0.75)     		17%
    ( to )
    urine chloride <10 mmol/l 9 0 inf
    (6.9 to inf)     		100%
    ( to )
    urine chloride 10-20 mmol/l 8 5 3.6
    (1.3 to 9.7)     		62%
    ( to )
    urine chloride >20 mmol/l 4 42 0.21
    (0.088 to 0.52)     		9%
    ( to )
    fractional excretion of sodium =1% 18 4 10
    (3.9 to 26)     		82% 0.16
    (0.055 to 0.45)     		7%
    fractional excretion of chloride =1% 20 2 22
    (5.8 to 87)     		91% 0.050
    (0.0073 to 0.34)     		2%
    total 21 47

    Comments

    1. Some patients with prerenal azotemia are nonoliguric; it is not possible to distinguish these patients clinically at the time of deciding whether or not to perform this diagnostic test. The inclusion of only oliguric patients in the definition of prerenal azotemia may have improved the apparent properties of the test.
    2. This test appears only of marginal assistance in differentiating renal from prerenal failure

    Citation

    1. Anderson RJ, Gabow PA, Gross PA: Urinary chloride concentration in acute renal failure. Mineral Electrolyte Metabolism 1984; 10: 92-97
    Search Terms: kidney failure, acute; sodium/urine or osmolality using sensitive strategy for studies of diagnostic tests (Haynes)
    Contributor: Catherine Clase, Chris Ball and Clare Wotton, April 2000
    Reviewer: Donald Stanley

    Clinical Question.
    Patient acute renal failure
    Intervention or Exposure urine sodium and chloride
    Comparison clinical prerenal azotemia
    Outcome diagnosis of prerenal failure