Increased renin concentration in plasma and amniotic fluid during storage.

Renin concentration was determined in plasma and amniotic fluid samples immediately after collection, after storage at -18 degrees C for up to 48 h, and after storage at 5 degrees C for as long as 48 h. Renin concentration increased, both in plasma (p less than 0.05) and amniotic fluid (P less than 0.02), after the storage at 5 degrees C, but no significant alteration occurred on storage at -18 degrees C. Partial activation of inactive renin could explain the observed increase in renin concentration at 5 degrees C.