On this page
- 17-hydroxyprogesterone in two units: the short answer
- What the test measures
- Why the units differ
- How to convert step by step
- 17-hydroxyprogesterone conversion chart
- 17-hydroxyprogesterone levels: what the numbers mean
- Interpreting 17-hydroxyprogesterone results
- When to see a doctor
- Frequently asked questions
17-hydroxyprogesterone in two units: the short answer
To convert 17-hydroxyprogesterone from ng/dL to nmol/L, multiply by 0.03026. To go back from nmol/L to ng/dL, multiply by 33.05 (or divide by 0.03026). For example, 500 ng/dL × 0.03026 = 15.13 nmol/L. The converter above works in both directions and shows where the result sits against typical reference ranges.
What the test measures
17-hydroxyprogesterone (17-OHP) is a steroid made on the way to cortisol. US labs report it in ng/dL; SI labs in nmol/L. With a molar mass of 330.5 g/mol, 1 ng/dL = 0.0303 nmol/L and 1 nmol/L = 33.0 ng/dL.
Why the units differ
17-OHP is the screening test for congenital adrenal hyperplasia (CAH), including the milder non-classic form that can cause irregular periods, acne and excess hair. Guideline cut-offs are given in both units.
Where the factor comes from
The conversion factor comes from the molar mass (330.46 g/mol) and the volume units on each side. Laboratories may round the factor slightly differently, which can change the last digit but never the clinical meaning.
How to convert step by step
- Check the unit printed next to the result on your report – ng/dL or nmol/L.
- ng/dL → nmol/L: multiply by 0.03026.
- nmol/L → ng/dL: multiply by 33.05.
- Round to the same number of decimals your lab uses.
Worked example in reverse: 4.54 nmol/L × 33.05 = 150.0 ng/dL.
17-hydroxyprogesterone conversion chart
| ng/dL | nmol/L |
|---|---|
| 50 | 1.51 |
| 100 | 3.03 |
| 150 | 4.54 |
| 200 | 6.05 |
| 300 | 9.08 |
| 500 | 15.13 |
| 800 | 24.21 |
| 1000 | 30.26 |
| 1500 | 45.39 |
| 3000 | 90.78 |
| nmol/L | ng/dL |
|---|---|
| 1.51 | 49.9 |
| 3.03 | 100.1 |
| 4.54 | 150 |
| 6.05 | 199.9 |
| 9.08 | 300.1 |
| 15.13 | 500 |
| 24.21 | 800.1 |
| 30.26 | 1,000 |
| 45.39 | 1,500 |
| 90.78 | 3,000 |
17-hydroxyprogesterone levels: what the numbers mean
| Category | ng/dL | nmol/L |
|---|---|---|
| Non-classic CAH unlikely (early-morning, follicular phase)<200 ng/dL ≈ <6 nmol/L | < 200 | < 6.05 |
| Indeterminate – stimulation test often advised | 200 – 1,000 | 6.05 – 30.26 |
| Highly suggestive of CAH>1,000 ng/dL ≈ >30 nmol/L | ≥ 1,000 | ≥ 30.26 |
Screening cut-offs as summarised in the Endocrine Society CAH guideline. Newborn screening uses different, age- and weight-adjusted thresholds.
Screening cut-offs as summarised in the Endocrine Society CAH guideline. Newborn screening uses different, age- and weight-adjusted thresholds.
Interpreting 17-hydroxyprogesterone results
In CAH an enzyme (most often 21-hydroxylase) is deficient, so 17-OHP builds up and is diverted into androgens. Classic CAH is detected by newborn screening. Non-classic CAH often shows up in teenagers or adults as irregular periods, acne, hirsutism or fertility problems and can look like PCOS, which is why 17-OHP is checked in that work-up. Timing matters: a sample taken in the afternoon or luteal phase can be falsely high.
A single result outside the reference range is common and often not significant on its own. Reference ranges are set so that about 1 in 20 healthy people fall outside them, and every laboratory sets its own limits for its method. Use the range printed on your report and discuss results with the clinician who ordered the test.
When to see a doctor
Contact your clinician if a result is flagged as abnormal and you have symptoms, if a value is far outside the range, or if results are changing over time. This page explains units; it cannot diagnose or replace medical advice.
Frequently asked questions
What is 6 nmol/L 17-OHP in ng/dL?
6 × 33.0 = 198 ng/dL.
When should 17-OHP be tested?
Early morning, and in women in the follicular phase (first week after a period), because levels rise after ovulation.
Can I use this converter for any lab?
Yes for the unit conversion, which is fixed by chemistry. Reference ranges differ between labs and methods, so compare your converted value with your own lab's range.