Androstenedione is a direct precursor of testosterone and oestrone, an oestrogen. It is produced from progesterone and DHEA. In women, it is synthesised in the adrenal gland and ovaries and in men in the testis. The largest proportion of androstenedione in the blood is bound with low affinity. The plasma levels of androstenedione are similar in women and men.
Increased concentrations of 17-OH progesterone and androstenedione are found in non-classic (late onset) congenital adrenal hyperplasia (CAH) with 21-hydroxylase deficiency. For monitoring of CAH, primarily 17-OH progesterone, androstenedione and testosterone are measured. For diagnostics of CAH in patients with polycystic ovary syndrome (PCOS), determination of androstenedione in serum is more sensitive than total testosterone.