Active and inactive renin in critically ill patients.

The relationship between active (A) and inactive (I) plasma renin concentrations (PRC) was examined in critically ill patients to test for intravascular renin activation in states of shock and tissue damage. Critically ill patients had significantly elevated APRC and lowered IPRC:APRC ratio compared with age and sex matched healthy subjects. IPRC in the critically ill was similar to the control group. During blood donation normal volunteers showed a twofold increase in APRC. The rise in APRC was proportionately greater than for IPRC, with a subsequent fall in IPRC:APRC ratio. In both critically ill patients and blood donors elevated APRC was associated with decreased IPRC:APRC ratio, consistent with either consumption of the inactive renin zymogen or preferential secretion of the active form. Individual critically ill patients displayed markedly depressed ratios but with only moderately elevated APRC, a pattern suggestive of intravascular renin activation. Consistent evidence for intravascular or extravascular activation of renin was not apparent.