Background: Measurements of total plasma cortisol (TPC) in the acute phase of aneurysmal subarachnoid haemorrhage (aSAH) have suggested a high incidence of adrenal insufficiency (AI).
Objective: To compare TPC and free plasma cortisol (FPC) measurements in acute aSAH and to assess whether rates of diagnosis of AI based on TPC and FPC criteria were discordant.
Methods: A prospective, observational study of 20 patients admitted within 7 days of aSAH to a tertiary intensive care unit. Cortisol binding globulin (CBG), TPC and FPC levels were measured at baseline, and cortisol profiles at 30 and 60 minutes after administration of 250_g corticotropin.
Results: Compared with controls, the mean baseline FPC (46 nmol/L [SD, 48 nmol/L] v 9 nmol/L [SD, 6 nmol/L], P<0.0001), and TPC (566 nmol/L [SD, 288 nmol/L] v 352 nmol/L [SD, 146 nmol/L], P=0.01) were significantly elevated with a greater proportional increase of FPC over TPC (6 v 1.2 times, P<0.0001). The relative increment of FPC compared with TPC in the patient group was 505% v 114% (P<0.0001) and in the control group was 662% v 145% (P<0.0001). The prevalence of AI, measured using TPC compared with FPC, was 30% v 0% (P=0.04).
Conclusion: In the acute phase after aSAH, the FPC increase is fivefold greater than that of TPC. There is discordance between TPC and FPC responses to corticotropin. The prevalence of AI, as assessed by FPC measurements, is negligible. We advocate caution in the assessment of adrenal cortical function using measurements of TPC in this population.