Acute renal failure: CT and ultrasound could help diagnose hydronephrosis.

Clinical bottom line (level 1b)

  1. A sixth of renal failure patients with suspected collecting system dilatation had it.
  2. In patients with acute or worsening renal failure, a positive CT scan helped diagnose dilatation (LR+11) , and so did a positive ultrasound (LR+6.2) .
  3. Absence of collecting duct dilatation on CT or ultrasound made the diagnosis much less likely.
Webb et al: Quarterly Journal of Medicine 1984; 211: 411-425
Expires April 2005

The study

Setting: teaching hospital, UK

91 patients (aged range 17 to 82 years; mean 56, ?% male) acute renal failure (creatinine >180 micromol/l or urea >15 mmol/l) or exacerbation of known chronic renal failure

Excluded if
  • renal transplant
  • nondiagnostic excretory urography
  • nondiagnostic CT scans (poor visualisation of kidneys and collecting system)
  • complicated appearances in the perinephric area that led to difficulty in interpretation



    • Independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
    Reference standard:
    • high dose excretory urography (performed after CT)- films at 0, 10, 30 minutes and then as required
    Diagnostic test: renal computed tomography (CT), without contrast- positive if intrarenal collecting system dilated; renal ultrasound

    The evidence

    pre-test probability of dilatation in CT patients: 14%, (95% CI: 8.2% to 21%)
    pre-test probability of dilatation in ultrasound: 17%, (95% CI: 11% to 24%)

    diagnostic test collecting system dilatation no dilatation LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    CT 18 0 11
    (5.9 to 19)     		64% 0.00
    (0.00 to 0.17)     		0.00%
    total 18 107


    diagnostic test collecting system dilatation no dilatation LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    ultrasound 26 0 6.2
    (4.1 to 9.2)     		57% 0.00
    (0.00 to 0.13)     		0.00%
    total 26 123

    Comments

    1. Since the publication of this paper improvements in imaging techniques have relegated intravenous urography to memory of older practitioners.
    2. Ct was nondiagnostic in 12/137 studies (9%). Ultrasound was nondiagnostic in 15/164 studies (9%).
    3. A final diagnosis of obstruction, on the basis of further investigations, clinical course and response to surgery, was made in 15 patients, all of whom had shown dilatation on CT and ultrasound.
    4. CT demonstrated the cause of the obstruction in 8/15 patients (53%), and ultrasound 5/15 (33%).
    5. Of the false positive CT examinations, 9 were described as mild hydronephrosis. Of the 20 false positive ultrasound examinations, 19 were described as mild hydronephrosis.

    Citation

    1. Webb JAW, Reznek RH, White FE, et al: Can ultrasound and computed tomography replace high-dose urography in patients with impaired renal function?. Quarterly Journal of Medicine 1984; 211: 411-425
    Search Terms: reference list
    Contributor: Catherine Clase, Chris Ball and Clare Wotton, April 2000
    Reviewer: Harold Szerlip

    Clinical Question.
    Patient acute renal failure
    Intervention or Exposure renal CT and ultrasound
    Comparison urography
    Outcome diagnosis of dilatation