CT Best for Diagnosing Obstructive Anuria
95% Accurate, 100% Sensitive
By Laurie Barclay, MD
WebMD Medical News
Reviewed by Gary D. Vogin, MD
June 10, 2002 -- Noncontrast computed tomography (NCCT) was 95% accurate and 100% sensitive in diagnosing ureteral obstructions in anuric patients, according to results of a study in the June issue of Urology. The standard protocol of combined KUB and ultrasound (US) was only 77% accurate.
"In patients with obstructive anuria, conventional KUB and US could not identify the cause of ureteral obstruction in about 40% of the patients," write Ahmed A. Shokeir, MD, PhD, and colleagues from Mansoura University in Egypt.
The authors compared NCCT and standard workup in 40 consecutive patients with obstructive anuria with an age- and sex-matched control group. Controls included the normal contralateral kidneys of 57 consecutive patients who had KUB, US, and NCCT for acute flank pain during the same study period. The gold standard for diagnosing the cause of obstruction was retrograde or antegrade ureterography with or without ureteroscopy or open surgery.
Because obstruction was bilateral in 8 patients and unilateral in 32, the study group comprised 48 renal units. Of 42 renal units with calculus obstruction, the site of stone impaction was identified in all renal units by NCCT and in only 25 by combined KUB and US. Sensitivity was therefore 100% for NCCT and only 59.5% for standard workup (P = 0.0001).
Of the 6 renal units with obstruction from other causes, both NCCT and US diagnosed the cause of obstruction in 3. The overall sensitivity was therefore 94% for NCCT and 58% for combined KUB and US (P = 0.0001). Although the specificity of NCCT was not significantly different from that of combined KUB and US (96.5% vs. 93%, respectively), the overall accuracy was 95% for NCCT and 77% for combined KUB and US (P = 0.0003).
Despite potential pitfalls in the interpretation of NCCT, the authors conclude that "the ability to diagnose a wide range of disease entities that result in flank pain remains a distinct advantage of NCCT."
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