To assess whether plasma renin activity (PRA) in patients with rheumatoid arthritis (RA) and evidence of renal involvement (microhematuria) can serve as potential marker of renovascular injury.
PRA was measured at rest and following exercise. All nonsteroidal antiinflammatory drugs or other medications that might affect renin release were stopped at least ten days prior to PRA measurements. PRA was correlated with the number of dysmorphic erythrocytes present in the urine sediment as indicators of glomerular capillary injury (microhematuria).
All patients with RA had a higher mean PRA than controls. Moreover, all patients with RA in whom microhematuria was present had a higher PRA than those without microhematuria. Simple and multiple regression analysis revealed a significant correlation between: a) PRA and rheumatoid factor levels; b) rheumatoid factor levels and the number of erythrocytes in the urine sediment; and c) PRA levels and the number of erythrocytes in the urine sediment.
The observations indicate that increased PRA may occur in normotensive patients with RA and no clinical or biochemical evidence of renal involvement. This may reflect activation of the renin-angiotensin system. The positive correlation between enhanced PRA, rheumatoid factor levels and microhematuria in RA patients may indicate inflammatory injury of the glomerular microvasculature involving the juxtaglomerular apparatus.