Free cortisol and free 21-deoxycortisol in the clinical evaluation of congenital adrenal hyperplasia

Context: Some patients with classic congenital adrenal hyperplasia (CAH) survive without glucocorticoid treatment. Increased precursor concentrations in these patients might lead to higher free (biological active) cortisol concentrations by influencing the cortisol-protein binding. In 21-hydroxylase deficiency (21OHD), the most common CAH form, accumulated 21-deoxycortisol (21DF), a precursor steroid, may further increase glucocorticoid activity. Both mechanisms could explain the low occurrence of symptoms in some untreated classic CAH patients. Objective: Establishment and validation of an LC-MS/MS method for (free) cortisol and (free) 21DF to quantify these steroids in untreated patients with classic CAH (n=29), non-classic CAH (NCCAH, n=5), other forms of adrenal insufficiency (AI, n=3), and controls (n=11) before and 60 minutes after Synacthen administration. Results: Unstimulated total cortisol levels of untreated classic CAH patients (median 109 nmol/L) were lower compared to levels in untreated NCCAH patients (249 nmol/L, p=0.010) and controls (202 nmol/L, p=0.016), but free cortisol concentrations were similar. Basal free 21DF levels were high in 21OHD patients (median 5.32 nmol/L) and undetectable in AI patients and controls (<0.19 nmol/L). After Synacthen administration, free concentrations of 21DF -but not cortisol- increased only in patients with 21OHD. Conclusions: Free cortisol levels were similar in classic CAH compared to controls and NCCAH patients, suggesting a comparable availability of cortisol. Additionally, 21OHD patients produce high levels of the glucocorticoid 21DF, possibly explaining the low occurrence of symptoms in some classic 21OHD patients. Free cortisol and (free) 21DF levels should be considered in the clinical evaluation of adrenal insufficiency in patients with CAH.