Endocrine Abstracts

Androstenedione and 17OHP are often used as measures of cortisol replacement in congenital adrenal hyperplasia (CAH) rather than cortisol itself. Very little is known of the dose response relationships between cortisol and A4 and 17OHP.

We have studied the relationship between 24 h serum cortisol, 17OHP and A4 in 33 (18M) children with CAH due to P450c21 deficiency. 24 h serum cortisol and 17OHP profiles were constructed using 20 min sampling intervals and expressed as the mean value. A4 was measured at 0800 h.

There was a significant relationship between mean 24 h serum 17OHP and A4 concentrations (r=0.62; P<0.001). For every 1 nmol/l rise in 17OHP, A4 rose by 0.2 nmol/l. Both mean 24 h 17OHP and A4 concentrations showed suppression when the 24 h mean cortisol concentration exceeded 150 nmol/l, although 50% showed suppression with a cortisol <150 nmol/l. This threshold was a step threshold and four S.D. below the mean 24 h cortisol production of normal individuals.

These data demonstrate that there are not equimolar changes in A4 and 17OHP, and that suppression of A4 and 17OHP occurs at cortisol concentrations that are below those associated with normal cortisol secretion. If only A4 and/or 17OHP are used to assess cortisol replacement it will leave many individuals under replaced with cortisol and at risk of Addisonian crisis.