Acute renal failure: urea:creatinine ratio was not very helpful in diagnosing prerenal failure.

Clinical bottom line (level 4)

  1. In patients with plasma urea more than 10 mmol/l, urea:creatinine ratios >0.1 marginally increased the chance of pre-renal failure. (LR+3.4) .
Morgan et al: British Medical Journal 1977; 2: 929-932
Expires August 2003

The study

Setting: university hospital, UK

131 patients (aged ?, ?% male) plasma urea >10 mmol/l (100 unselected, 17 with acute renal failure, 14 with chronic renal failure)

Excluded if
  • age <16 years
  • different plasma sample analysed for creatinine
  • under long term care of renal physicians



    • ?independent unblinded reference standard, applied in all patients from a consecutive inappropriate spectrum.
    Reference standard:
    • patients' history and clinical course taken from clinical records
    Diagnostic test: urea:creatinine ratio (positive if >1:10)

    The evidence


    diagnostic test pre-renal failure intrinsic renal failure LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    urea:creatinine >1:10 30 5 3.4
    (1.5 to 8.0)     		46% 0.53
    (0.38 to 0.74)     		12%
    total 54 31

    Comments

    1. Patient demographics and the severity of their renal failure were not reported.
    2. Cut-off point of 1:10 was chosen when re analysing the data as this corresponds approximately to the widely quoted 20:1 ratio expressed in non-SI units.
    3. Other studies have shown the incidence of prerenal failure in hospital patients is about 20%, making the post-test probability 46% if urea:creatinine >1:10, and 12% if urea:creatinine <1:10.

    Citation

    1. Morgan DB, Carver ME, Payne RB: Plasma creatinine and urea:creatinine ratio in patients with raised plasma urea. British Medical Journal 1977; 2: 929-932
    Search Terms: urea, creatinine, ratio, kidney failure, acute in Medline
    Contributor: Catherine Clase, Chris Ball and Clare Wotton, May 2000
    Reviewer: Catherine Clase

    Clinical Question.
    Patient plasma urea >10 mmol/l
    Intervention or Exposure urea:creatinine ratio
    Comparison history and clinical course
    Outcome diagnosis of pre-renal failure