Background: Standard assays for serum cortisol measurements determine total cortisol (TC) concentrations but not the unbound biologically active serum free cortisol (sFC). Measurement of TC would be greatly influenced by alteration in cortisol-binding globulin (CBG) concentrations. It is, therefore, important to determine sFC levels when CBG levels are either decreased or increased.
Objective and hypotheses: To determine basal and glucagon-stimulated sFC in relation to TC, GH and glucose levels in children.
Method: Infants and children referred for evaluation of GH and cortisol reserve, underwent glucagon test. Baseline and stimulated serum TC, FC, GH and glucose levels were measured before and every 30 min for 180 min after IM administration of Glucagon (30 mcg per kg, max of 1 mg). Serum TC and GH were determined by chemiluminescence and serum FC was measured by the same method following equilibrium dialysis. A TC response of 20 mcg/dl was considered normal.
Results: The study group consisted of 62 subjects (26 girls), median age 3.9 years (range, 0.513.8). Mean baseline TC and sFC levels were 12.9±6.5 mcg/dl and 0.78±1.1 mcg/dl respectively. Mean peak TC and sFC levels (150 min) were 29.2±9.5 mcg/dl and 1.7±1.3 mcg/dl respectively. Mean fractions of sFC at baseline and at peak were 4.3±1.6% and 5.2±1.7% reflecting a lower increase in TC (200%) compared to sFC (250%). peak TC and sFC levels were positively correlated (r=0.5 P<0.001). The girls had a higher peak TC and Peak sFC P=0.004 and P=0.03 respectively. There was a negative correlation between peak TC and age r=−0.3, P=0.02, however no correlation was found between peak sFC and age r=−0.06, P=0.7.
Conclusion: Based on these findings, we suggest pilot normal ranges for basal and glucagon-stimulated sFC for children. These norms might serve as a reference when cortisol binding globulin are abnormal. The finding that TC is age dependent while the sFC is not may suggests that the sFC is superior to TC measurement in paediatric population. The higher TC and FC in girls compared to boys might suggest an survival advantage.
01 Oct 2015 - 03 Oct 2015