Endocrine Abstracts

Background: There is currently no agreed consensus for the optimization and titration of mineralocorticoid (MC) therapy in patients with primary adrenal insufficiency (PAI).

Objective: To measure serum (sFC) and urine (uFC) fludrocortisone levels and explore their relationship with biochemically and clinically important variables (including treatment compliance) in order to evaluate their usefulness as markers to guide the MC replacement titration.

Methods: Multi-centre, observational, cross-sectional study on 41 patients (median age 39 years, IQR 27-56) with PAI on MC replacement therapy (median dose 100 mg/d, range 50-400). sFC and uFC levels (measured by LC-MS/MS), plasma renin concentration (PRC), electrolytes (Na⁺, K⁺), mean arterial blood pressure (MAP), total daily Glucocorticoid (dGC, hydrocortisone equivalents) and MC (dMC) dose, anthropometrics and assessment of GC and MC treatment compliance were incorporated into statistical models.

Results: We observed a close relationship between sFC and uFC (r=0.434, P=0.005) as well as between sFC and the time from the last FC dose (r=-0.355, P=0.023). Total daily MC dose was related to dGC dose (r=0.556, P<0.001), K⁺ (r= -0.388, P=0.013) as well as sFC (r=0.356, P=0.022) and uFC (r=0.531, P<0.001) levels. PRC was related to Na⁺ levels (r=0.517, P<0.001) and MAP (r=-0.427, P=0.006), but not to MC dose, sFC or uFC . Multiple linear regression analyses did not support a role for sFC, uFC or PRC measurements and confirmed K⁺ (B=-44.593, p=0.005) as the most important variable to guide dMC titration. However, when compliance was inserted into the model, it was the only factor affecting dMC.

Conclusions: sFC and uFC levels are not helpful in dMC titration in PAI. Clinicians should continue to rely on clinical and biochemical important variables (electrolytes, blood pressures and symptoms) to guide their decisions on MC dose adjustment, being aware that patient’s compliance to treatment is a major contributor for the reliability of such clinical markers.