What Does the 17-Hydroxyprogesterone (17-OHP) Test Measure?
The 17-hydroxyprogesterone (17-OHP) test measures serum or dried blood spot levels of 17-hydroxyprogesterone, a steroid hormone primarily used to screen for and diagnose congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, and to monitor treatment adequacy in patients with this condition. 1, 2
Primary Clinical Application: Congenital Adrenal Hyperplasia
- 17-OHP is the key diagnostic marker for 21-hydroxylase deficiency, the most common form of CAH, where enzyme blockage causes accumulation of this precursor steroid 2, 3
- Normal values in children are less than 1.1 μg/L (3.3 nmol/L), while untreated CAH patients show values up to several hundred μg/L—representing a dramatic elevation that makes this test highly sensitive 2
- For bilateral adrenal incidentalomas, guidelines specifically recommend collecting 17-OHP levels to rule out congenital adrenal hyperplasia 4, 1
Diagnostic Performance
- In CAH screening, 17-OHP shows superior sensitivity compared to traditional markers: the rise in 17-OHP is much more pronounced than the 15-25 fold increase seen in 17-ketosteroids and pregnanetriol 2
- LC-MS/MS methodology achieves 100% clinical sensitivity and 96.4% specificity when using a cutoff value of 17-OHP >39.1 ng/mL in dried blood spot samples 5
- Immunoassays produce high rates of false positives due to matrix effects, particularly in patient samples, making LC-MS/MS the preferred confirmatory method 5
Monitoring Treatment in CAH
- 17-OHP levels respond dynamically to treatment: they rise after ACTH stimulation and are suppressed by dexamethasone or cortisone treatment, making them valuable for therapeutic monitoring 2
- Home monitoring using dried filter paper blood samples is reliable and practical (correlation r=0.98 with venous samples), allowing assessment of adrenal suppression patterns throughout the day to optimize hydrocortisone dosing 6
- Blood sampling at different times reveals patterns of 17-OHP secretion and identifies specific times when adrenal suppression is inadequate, facilitating targeted dose adjustments 6
Important Testing Considerations
- Multiple courses of antenatal corticosteroids decrease 17-OHP values by approximately 30% in preterm infants, raising the risk of false-negative results in newborn screening programs 7
- Single courses of prenatal steroids do not significantly affect 17-OHP levels, but multiple courses do produce clinically significant suppression 7
- Dried blood spot samples remain stable for at least 2 weeks under various storage conditions, making them practical for screening programs 6
Clinical Context: Not for Preterm Birth Prevention
- 17-OHPC (17-alpha hydroxyprogesterone caproate) is a synthetic progestogen medication—completely different from the 17-OHP diagnostic test—that was previously used for preterm birth prevention but has been withdrawn from the market due to lack of efficacy 4, 8
- The FDA withdrew approval of 17-OHPC on April 5,2023, and guidelines now recommend against its use, including compounded formulations, for treatment of short cervix 4