Abstract

A semi-micro method for determination of plasma renin activity (PRA) by radioimmunoassay of generated angiotensin I (AI) is described. The method permits measurement of PRA on 250 mul of plasma without loss of specificity, sensitivity, accuracy or preision. The small sample size has considerable application in terms of investigation of infants and young children. A reference range was established for healthy children on free diets. There was a 15-fold decline in PRA with age from a mean value of 1404pgAI/ml h-1 (ngAI/1. h-1) in infancy to a mean of 85 pgAI/ml h-1 (ngAI/1. h-1) in adult life.