High Prevalence of “Biochemical” Adrenal Insufficiency in Thalassemics: Is It a Matter of Different Testings or Decreased Cortisol Binding Globulin?

Abstract

High prevalence of "biochemical" adrenal insufficiency (AI) in thalassemics has been reported. However, "clinical" AI is rare. The aim was to determine whether cortisol binding globulin (CBG) or tests used in assessing adrenal function contributed to the abnormally high prevalence of biochemical AI. The study was conducted at Ramathibodi Hospital, Mahidol University, Bangkok, Thailand. Participants included 56 children and adolescents with thalassemia and 44 controls. Serum CBG and adrenal function test results assessed by 1 μg cosyntropin test and insulin tolerance test (ITT) were measured. Free cortisol index (FCI) calculated by total cortisol (TC)/CBG and calculated free cortisol (cFC) were determined. Mean (sd) CBG levels were comparable between patients and controls [45.2 (11.0) vs. 47.0 (8.6) mg/liter]. Peak TC, FCI, and cFC after cosyntropin test were lower in thalassemics [TC, 15.2 (4.0) vs. 18.9 (3.1) μg/dl; FCI, 3.4 (0.8) vs. 4.2 (1.2) μg/mg, P <0.001; and cFC, 1.03 (0.38) vs. 1.44 (0.61) μg/dl, P = 0.008]. Thirty of 56 thalassemics (53.6%) had AI, defined as having peak TC of less than 16 μg/dl. ITT was performed in 26 of those 30 patients. Five of 26 patients had peak TC after an ITT of at least 20 μg/dl. As a result, the estimated frequency of AI in the entire patient group was reduced by approximately 10%. The 1 μg cosyntropin test could be an adrenal function screening test in thalassemics. However, for definite diagnosis, ITT should be performed in those having peak total cortisol of less than 16 μg/dl after the 1 μg cosyntropin test.