How to prepare for the ‘Progesterone’ test: rules for taking it

Progesterone is the hormone of the corpus luteum, and most often it is measured to confirm that ovulation has occurred. But it is precisely with progesterone that patients most often ‘miss’ the right day: the standard recommendation ‘on day 21’ does not suit everyone. The editorial team explains how to correctly calculate the date of the test, what affects the result and how it is interpreted.

The role of progesterone and indications for the test

Progesterone in women is produced mainly by the corpus luteum, which forms in place of the follicle after ovulation. The hormone prepares the endometrium for embryo implantation, supports early pregnancy and has a number of systemic effects — in particular, it raises basal body temperature. A small amount of progesterone is formed in the adrenal glands, and in pregnant women the placenta later becomes the main source.

Before ovulation the progesterone level is low. After it, it rises, reaches a maximum roughly in the middle of the luteal phase and decreases before menstruation if pregnancy has not occurred. It is on this that the main use of the test is based — confirming ovulation.

The NICE guideline on fertility problems (CG156) recommends that women with a regular cycle measure progesterone in the middle of the luteal phase to confirm ovulation. A similar approach is described in the ASRM committee opinion on the diagnostic evaluation of an infertile woman.

The test is also used in cycle disorders, in assisted reproductive technology programmes, in assessing early pregnancy in certain clinical situations, and when examining for some disorders of the adrenal cortex.

How to correctly choose the day of the draw

The well-known advice to ‘take progesterone on day 21’ applies only to a 28-day cycle. The logic here is as follows: ovulation is around day 14, and the middle of the luteal phase is about 7 days after it. In a woman with a longer or shorter cycle, ‘day 21’ may fall at a completely different moment.

It is more correct to count from the expected menstruation: the luteal phase is relatively stable in duration, so the optimal draw is about 7 days before the next period. For example, with a 35-day cycle this will be around day 28, with a 24-day cycle — around day 17.

If menstruation began earlier or later than 7 days after the test, the result may be uninformative: the blood was probably taken not in the middle of the luteal phase. In that case the doctor may suggest repeating the test in the next cycle.

You can also go by an ovulation test: if an LH peak was recorded, progesterone is taken about 7 days after it.

Pulsatile secretion and repeat measurements

Progesterone in the luteal phase is released unevenly. A study by Filicori and colleagues (1984) showed the pulsatile nature of progesterone secretion by the corpus luteum, linked to LH pulses. Because of this, the hormone concentration may differ noticeably even over the course of a few hours.

For practice this means that a single value in the borderline zone is not grounds for a conclusion about ‘luteal phase insufficiency’. The work of Wathen and colleagues (1984) demonstrated the limitations of a single progesterone measurement for assessing the quality of the luteal phase.

At the same time, for the simple confirmation of the fact of ovulation, a single correctly calculated test is usually sufficient. In clinical practice a threshold of about 3 ng/mL (approximately 10 nmol/L) is often cited: a value above it indicates that ovulation has probably occurred. The specific thresholds depend on the laboratory and clinical recommendations.

• take it at the same time of day for repeat measurements, preferably in the morning;
• the day before — usual sleep, without intense training or alcohol;
• indicate on the referral the day of the cycle and the expected date of menstruation;
• report all hormonal drugs, ovulation stimulation, biotin.

For conversion: 1 ng/mL of progesterone corresponds to approximately 3,18 nmol/L. When comparing results from different sources, always pay attention to the units.

Drugs, pregnancy and special situations

Hormonal contraception suppresses ovulation, so against its background a test for the body's own progesterone is uninformative. The synthetic progestins in the tablets, as a rule, are not measured by standard progesterone tests or are measured incorrectly.

In contrast, micronized progesterone, which is prescribed in reproductive medicine and during pregnancy, is identical to the natural one and is reflected in the test. Its blood level depends on the route of administration: with vaginal use the serum concentration may not reflect the concentration in the uterine tissues. Therefore the assessment of the effectiveness of such therapy is made by a doctor.

During pregnancy progesterone rises, and it is interpreted by separate criteria. In some clinical scenarios of early pregnancy the progesterone level is used as an auxiliary indicator, but conclusions are always drawn together with hCG and ultrasound.

Biotin in high doses may affect progesterone immunoassays; the FDA has warned about false laboratory test results due to biotin. It is worth informing the laboratory about the intake of such supplements.

Ovulation stimulation, hCG drugs, gonadotropins and other reproductive medicine agents alter the progesterone level. In these cases the doctor draws up the test schedule in accordance with the treatment protocol.

Progesterone in men and athletes

In men progesterone is present in low concentrations and is formed mainly in the adrenal glands and testes as an intermediate link in steroid synthesis. It is not measured routinely; the test is ordered for specific indications, in particular when examining for disorders of steroidogenesis.

In the sports community, progesterone is sometimes mentioned in connection with gynecomastia and the intake of 19-nortestosterone derivatives. It should be understood that progesterone concentrations in men are low, and ordinary immunoassays in this range may be insufficiently accurate — similarly to estradiol.

If a doctor does nevertheless order this test for a man, the general rules apply: a morning draw, a stable state, no intense training the day before, with a report on all hormonal agents.

In female athletes with an energy deficit and excessive loads, ovulation is often disrupted. Low progesterone in the middle of the luteal phase in such a case may be a manifestation of anovulation associated with training load and nutrition, rather than a separate ‘hormonal disease’.

Editorial conclusions

The main rule of the progesterone test is the right day. To confirm ovulation, blood is taken in the middle of the luteal phase, about 7 days before the next menstruation, rather than mechanically ‘on day 21’.

Progesterone is secreted in pulses, so borderline results should be assessed with caution and, if necessary, repeated. Hormonal drugs, contraception, pregnancy and biotin alter the interpretation.

Conclusions about ovulation, fertility or therapy are made by a gynecologist or reproductive specialist.

We also advise reading our articles on preparing for the estradiol, LH and FSH tests.

References

1. National Institute for Health and Care Excellence. Fertility problems: assessment and treatment. Clinical guideline CG156. London: NICE; 2013.
2. Practice Committee of the American Society for Reproductive Medicine. Diagnostic evaluation of the infertile female: a committee opinion. Fertil Steril. 2015;103(6):e44–e50.
3. Filicori M, Butler JP, Crowley WF Jr. Neuroendocrine regulation of the corpus luteum in the human: evidence for pulsatile progesterone secretion. J Clin Invest. 1984;73(6):1638–1647.
4. Wathen NC, Perry L, Lilford RJ, Chard T. Interpretation of single progesterone measurement in diagnosis of anovulation and defective luteal phase: observations on analysis of the normal range. Br Med J (Clin Res Ed). 1984;288(6410):7–9.
5. Strauss JF, Barbieri RL (eds). Yen & Jaffe's Reproductive Endocrinology. 8th ed. Elsevier; 2019.
6. U.S. Food and Drug Administration. The FDA warns that biotin may interfere with lab tests: FDA safety communication. 2017.