The value of ultrasound as a screening procedure for urological disorders in renal failure

Renal ultrasound was evaluated as a screening procedure for urological conditions (hydronephrosis or space-occupying lesions) in 175 patients (316 kidneys) with renal failure. The final diagnosis of renal disease was based on excretory urography, ascending or translumbar pyelography, open surgical findings, clinical and laboratory test results or renal biopsies. Ultrasonic images suggestive of renal disease requiring surgery were obtained in 83 kidneys and subsequently confirmed in 67. There were 16 falsely positive and 2 falsely negative results. Assuming a 22 per cent prevalence of renal disease requiring surgery in the azotemic population, Bayes' theorem predicts that an abnormal ultrasonic test will increase the probability of surgery in a patient with renal failure from 0.22 to 0.81, while a negative test will reduce the probability from 0.22 to 0.013. Renal ultrasound is a highly effective method to screen for patients with renal failure who require contrast studies. With this means the risks and cost of contrast investigations can be reduced markedly.