Replacement mineralocorticoid(MC)therapy in patients with primary hypoadrenalism is titrated according to clinical and /or biochemical criteria. No single objective assessment is adequate for monitoring,though targets for plasma renin and serum electrolyte concentrations and blood pressure(BP)have been proposed.Plasma renin concentrations within the middle to upper normal range would suggest adequate MC replacement. We reviewed the case notes of 18 patients in order to identify the major determinants of MC replacement,specifically the extent to which treatment was modified on the basis of plasma renin concentration. Simultaneous measurement of plasma renin,serum electrolytes and BP had been recorded in 16 out of 18 patients. In only 1/16 patients,were the most recently recorded plasma renin, serum potassium and BP values within the suggested target ranges.In the remaining patients,recorded plasma renin concentration were elevated in 8/16 and low in 7/16 patients. Within the group of patients with an elevated plasma renin,4 had simultaneous low resting BP or significant postural BP fall,3 had BP within the target range and 1 had normal BP. The 7 patients with low plasma renin had normal electrolytes and BP,2 had raised systolic BP and one had BP within the normal range. Seven patients out of the 16 (43%) therefore had plasma renin values outside the target range (3 high,4 low )but normal serum electrolytes and BP values.
Modifications to MC therapy were made when serum electrolytes were abnormal or there was evidence of symptomatic postural drop in BP,but in no patients was the dose of MC modified as a result of plasma renin concentration alone. All 18 patients remain asymtomatic based on their most recent clinic appraisal.We question whether plasma renin could add anything significant to the management of primary hypoadrenalism.