MEASUREMENT OF LOW-LEVELS OF PLASMA-RENIN ACTIVITY - A METHODOLOGICALIMPROVEMENT

Background: The present method to measure plasma renin activity is cum bersome and imprecise, factors that limit its clinical application. Ai m: To assess the importance of blood sampling conditions and the usefu lness of increasing incubation time to measure plasma renin activity a t low levels. Patients and methods: Twenty hypertensive patients, 14 f emale, aged 14 to 76 years old, were studied. Two blood samples were o btained after a 10 min rest in the sitting position and after a 30 min rest in supine position. One blood sample of each condition was sent to the laboratory at room temperature and the other sample was sent re frigerated. Angiotensin I concentration was determined after 3 h of en zymatic incubation at 37 degrees C and, in subjects with an activity o f less than 1 ng/ml/h, after 18 h of incubation. Results: No significa nt differences in plasma renin activity were observed between the samp les obtained with different rest times or different transportation met hods. In people with low plasma renin activity, the 18 h enzymatic inc ubation reduced the lower detection from 0.3 to 0.014 ng/ml/h and the coefficient of variation from 14.4 to 3.2%. Conclusions: A simplified blood sampling method does not change plasma renin activity values, an d the longer enzymatic incubation in people with low plasma renin acti vity improves both the sensitivity and accuracy of the determination.