Interobserver agreement on captopril renography for assessing renal vascular disease

Captopril-stimulated renography is widely used to screen selected groups of hypertensive patients for renal vascular disease. Evaluation of the test is a complex task. Lack of interobserver agreement on the assessment and interpretation of renographic parameters may contribute to differences in sensitivity and specificity between studies. Methods: Three experienced nuclear medicine physicians evaluated 658 renograms of 503 hypertensive patients suspected of having renal vascular disease from a large Dutch multicenter study (the Dutch Renal Artery Stenosis Intervention Cooperative [DRASTIC] study). Interobserver agreement on several renographic parameters was assessed by the K statistic and the intraclass correlation coefficient (ICC). Results: The interobserver agreement on the time to excretion was high: The pooled ICC was 0.90. The pooled K was ≥0.65 for the pattern of the time-activity curves, the visual aspect of the scintigraphic images (visible uptake and kidney size), and the judgment on the presence of renal artery stenosis. However, the interobserver agreement on cortical retention and pelvic retention by visual inspection of the images was rather low (pooled K = 0.46 and 0.52, respectively). Pelvic retention was found to complicate the interpretation of renography. Conclusion: Interobserver agreement on most of the renographic parameters was satisfactory, but the assessment of cortical retention was more difficult, in particular, in the presence of pelvic retention. Captopril renography should be interpreted with caution if pelvic retention is suspected. Interobserver variability offers one of several explanations for the differences in diagnostic test performance that are found between studies.