NEW YORK (Reuters Health) - Noncontrast helical CT (NHCT) scanning is a more accurate method of diagnosing acute urolithiasis than intravenous pyelogram (IVP), according to researchers who conducted a meta-analysis of previously published data.

Since its introduction in 1923, intravenous pyelography (IVP) has been the test of choice for diagnosing acute urolithiasis, the researchers explain. However, in 1994, NHCT was introduced as a possible replacement for IVP.

The benefits of NHCT over IVP include no exposure to IV contrast, the ability to visualize radiolucent stones and evaluate disease outside the urinary tract, and a shorter examination time, the investigators note. Individual studies comparing the two test methods have consistently yielded findings favoring NCHT, but no formal data has been conducted, they report in the September issue of the Annals of Emergency Medicine.

Dr. Andrew Worster, from Hamilton Health Sciences Corp. in Ontario, Canada, and colleagues conducted a meta-analysis of data from four studies that compared the two tests in patients with suspected acute urolithiasis. Data from a total of 296 patients were included in the analysis.

The researchers found that NCHT was significantly better than IVP at ruling in and ruling out acute urolithiasis. The pooled positive likelihood ratios for NCHT and IVP were 23.15 and 9.32, respectively. The corresponding negative likelihood ratios were 0.05 and 0.33. Differences between NCHT and IVP were statistically significant. Furthermore, no significant differences were noted between the results of any of the four studies.

"The results of this meta-analysis show NCHT to be significantly more accurate than IVP in evaluating patients with suspected acute urolithiasis," Dr. Worster and his colleagues state. But because NCHT was conducted before IVP in all four studies, the patient may pass the stone after NCHT and before IVP, possibly biasing the studies in favor of NCHT, they add.

"At the time of this study, no randomized controlled trials comparing NHCT with IVP for the diagnosis of acute urolithiasis have been conducted," the authors point out.

Ann Emerg Med 2002;40:280-286.

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