Plasma Renin: A Useful Marker for Mineralocorticoid Adjustment in Patients With Primary Adrenal Insufficiency.

Context: Renin is a marker of blood volume. There is no consensus on the validity of plasma renin measurement for adjusting mineralocorticoid (MC) substitution in patients with primary adrenal insufficiency (PAI).

Objective: This work aimed to investigate if plasma renin could be used to adjust MC substitution in patients with PAI.

Methods: A total of 150 patients with at least one measurement of plasma renin followed for PAI at 2 tertiary expert centers between 2008 and 2022 were retrospectively included. As supraphysiological hydrocortisone might have additional MC activity, we integrated the individual hydrocortisone dose to obtain the MC equivalent dose (Eq-MC). Renin less than 20 mIU/L was considered oversubstituted, renin between 20 and 60 mIU/L as correctly substituted, and renin over 60 mIU/L as undersubstituted.

Results: The mean dose of fludrocortisone was 82.3 ± 46 μg/day. Plasma renin was abnormal in 56.7% of cases (7 patients oversubstituted and 78 patients undersubstituted). Abnormalities in electrolyte levels were observed in only 12.7% of patients. Plasma renin correlated negatively with sodium (P < .01) and systolic blood pressure (P = .026), and positively with potassium (P < .01). Doses changes in Eq-MC had a statistically significant effect on renin levels (P = .0037), with an increase of MC dose correlating with a decrease in renin level and vice versa; no correlation was observed using electrolytes or blood pressure.

Conclusion: Plasma renin correlates with electrolytes and blood pressure. While dose changes significantly alter renin levels, electrolytes and blood pressure do not, suggesting that renin may provide more information about MC replacement therapy than electrolytes and blood pressure.