For years the demonstration of a metabolic defect and its location depended upon the study of urinary steroid excretion. Today, the immunoassay of blood 17-hydroxy-progesterone (17-OHP) has become the primary assessment for the diagnosis and management of congenital adrenal hyperplasia. With the 21-hydroxylase and H??-hydroxylase deficiencies, the 17-OHP level will be 50-400-fold above normal.
During delivery of affected infants, the concentration of 17-OHP is elevated in cord blood (1,000-3,000 ng/dL [30-90 nmol/L]), but it rapidly decreases to 100-200 ng/dL (3-6 nmol/L) after 24 hours. A delay in measurement gains accuracy. In contrast to 17-ketosteroids in the urine where the delay must be several days, with 17-OHP the delay need be only a day or two. In affected infants, 17-OHP ranges from 3,000 to 40,000 ng/dL (90-1,200 nmol/L). Measurement of 17-OHP is the basis for the newborn screening programs currently in place in many countries and some states in the U.S.

In adults, 17-OHP must be measured first thing in the morning to avoid later elevations due to the diurnal pattern of ACTH secretion. The baseline 17-OHP level should be less than 200 ng/dL (6 nmol/L). Levels greater than 200 ng/dL, but less than 800 ng/dL (24 nmol/L), require ACTH testing (discussed in Chapter 14). Levels over 800 ng/dL (24 nmol/L) are virtually diagnostic of the 21-hydroxylase deficiency. The DHAS level is usually normal. The hallmarks of late-onset adrenal hyperplasia are elevated levels of 17-OHP and a dramatic increase after ACTH stimulation. The elevated levels of 17-OHP are often not impressive (e.g. overlapping with those found in women with polycystic ovaries due to anovulation), and a simple ACTH stimulation test must be utilized.

Of course, in patients with 3 ??-hydroxysteroid dehydrogenase or 17-hydroxylase blocks, the 17-OHP level will not be elevated. With the 3??-hydroxysteroid dehydrogenase block, the blood levels of DHA and DHA sulfate (DHAS) will be markedly increased. In the 11 ??-hydroxylase deficiency, in addition to elevated 17-OHP, elevation of 11-deoxycortisol is diagnostic. In this deficiency, plasma renin activity will be little, whereas in 21-hydroxylase and 3 ??-hydroxysteroid dehydrogenase deficiencies plasma renin activity is elevated in the salt losing forms.