Interpretation of captopril renography by nuclear medicine physicians

This study was designed to assess intra- and interobserver variability and diagnostic accuracy of nuclear medicine physicians in their evaluation of baseline and captopril renograms.

The diagnostic performance of three experienced nuclear medicine physicians according to their interpretation of baseline, captopril and paired renograms was assessed. To this end, the readers evaluated the renograms of 28 hypertensive patients in whom a diagnosis of renovascular hypertension was suspected on the basis of clinical clues. All patients also underwent angiography. The readers were unaware of the angiographic diagnosis.

Thirteen of 28 patients proved to have renal artery stenosis (8 unilateral, 5 bilateral) on renal angiography. The concordance in the renographic diagnoses between the three readers was reasonably good, with an intraobserver agreement and kappa (observed agreement corrected for chance) ranging from 64% to 89% and from 0.52 to 0.75, respectively, and an interobserver agreement and kappa ranging from 68% to 86% and from 0.61 to 0.82. The sensitivity of their interpretation of paired baseline plus captopril renograms in relation to the angiographic diagnosis is poor and below 50%. The post-test probability of RAS in case of a negative renographic study was found to be rather similar to the pre-test probability (prevalence) of 46%. Blinding readers to which renogram was obtained after captopril imaging increased their accuracy.

The intra- and interobserver agreement between experienced nuclear medicine physicians who evaluate renograms was found to be reasonably good. Blinding readers as to which renogram is the pre- and post-captopril image seems to enhance their diagnostic accuracy in instances of positive scans.