ABSTRACTS PRESENTADOS AL 11th INTERNATIONAL SYMPOSIUM "RADIONUCLIDES IN NEPHRO-UROLOGY", REALIZADO EN MONTEREY, CALIFORNIA, 13-17 MAYO 2001.

Roland Müller-Suur, Per Bjellerup, Jan Svensson, Thomas Kahan

Karolinska Institute Danderyds Hospital, Division of Clinical Physiology Clinical Chemistry and Internal Medicine, Stockholm, Sweden.

roland.muller-suur@fys.ds.sll.se

Assay of plasma renin levels may be useful in patients undergoing captopril renography in order to support or exclude renin dependent renovascular hypertension. Recently a new rapid (one day analysis) and simple method using immunoradiometric assay or renin (IRMA) have been introduced in contrast to the more complicated time consuming enzymatic plasma renin activity measurement (PRA). Since IRMA not only measures renin but partly also prorenin, the question of its reliability arise.

Method: In 77 consecutive hypertensive patients we analyzed the plasma renin levels using both methods for comparison. The patients were asked to stop their antihypertensive medications 3 days before the test. Blood samples were taken at rest and 60 minutes after ingestion of 50 mg captopril. Seven of the patients had renovascular hypertension according to angiography or positive captopril renography.

Results: The plasma renin levels varied from 0 to 359 ng/l using the IRMA method and from 0 to 65 ng Al/ml h using the PRA method. The values correlated linearly, R= 0.86, irrespectively whether taken at rest or after captopril. Analyzing the regression coefficient only in the 7 renovascular hypertensive patients with high renin levels (IRMA values from 26 to 359 and PRA values from 7.1 to 65) a high R=0.75 was observed. Analyzing the correlation in patients (n=37) with PRA lower than 1 ng Al/ml h no linear correlation was found, R=0.19. The activation and possible cross reaction of prorenin seems to play a larger role in samples with low renin.

We conclude that the rapid IRMA renin assay correlates well to the reference method (PRA) at levels >1 ng Al/ml h. However in patients with expected low levels as in hyperaldosteronism IRMA cannot be recommended since it does not correlate well to the reference method. In such cases the PRA assay has to be used.