6 min - BioSense Team - 2026-10-21
- level:understanding
- pilule et prise de sang
- contraception bilan sanguin
- pilule résultats analyses
- pilule cholestérol triglycérides
The combined birth control pill and other combined hormonal contraceptives can change several blood test results, sometimes markedly, with no disorder involved. The markers affected include cortisol, total thyroid hormones, testosterone, triglycerides and CRP, and in some formulations gamma-GT, most often because the liver makes more transport proteins. Telling your doctor and the lab about your birth control means these results can be read correctly.
You have been on the pill for years and you no longer think about it. On your latest blood test, one or two lines fall outside the range and you are trying to understand why.
Combined estrogen-progestin birth control changes several test results through a well-identified mechanism, without the parameter concerned being genuinely disturbed in your body.
Why birth control changes blood test results: transport proteins
Many hormones do not circulate freely in the blood. They travel bound to transport proteins, made by the liver. Only the small unbound fraction is active.
Most combined pills contain a synthetic estrogen, ethinyl estradiol. It stimulates the liver's production of several proteins, including these transport proteins.
Three of them rise markedly:
- SHBG, which transports the sex hormones.
- CBG, which transports cortisol.
- TBG, which transports the thyroid hormones.
Yet many common assays measure the total hormone, that is, the free fraction and the bound fraction added together. When the transport protein rises, the total amount measured rises as well, while the active fraction may not have moved.
That is the essence of the phenomenon. The number goes up, and the underlying biology can stay stable.
Which blood test markers does birth control change?
High cortisol on the pill
Total cortisol measured in the blood is higher on combined birth control. In a randomized trial of 121 healthy women, total cortisol and CBG rose on both pills tested, with a greater rise on the ethinyl estradiol pill than on an estradiol pill.
The practical consequence is important. If excess cortisol (Cushing's syndrome) is being looked for, a first-line test can come back falsely abnormal in someone on the pill. The Endocrine Society lists estrogens among the drugs that raise CBG and may falsely elevate cortisol results, and the 2021 international consensus notes that the dexamethasone suppression test may not be reliable with oral estrogen. MedlinePlus adds that you may be told to temporarily stop estrogen before a cortisol test. Only your doctor can decide that, and other tests may be chosen instead, such as late-night salivary cortisol.
Thyroid hormones on the pill: total T4 and T3, TSH
Total T4 and total T3 rise on birth control, since they include the fraction bound to the transport protein. The American Thyroid Association recommends relying on TSH and free T4 in this situation, and these are typically in the normal range. The same trial found no relevant change in TSH or free T4.
In other words, a total T4 above the range on the pill does not mean a thyroid disorder.
Low testosterone on the pill
Two effects add up: the pill slows androgen production, and the rise in SHBG captures more testosterone. A 2014 meta-analysis found that free testosterone falls about twice as much as total testosterone.
A testosterone test done on combined birth control is therefore hard to interpret, and that information must accompany the result.
Gamma-GT on the pill
Results vary by formulation. In a study of 1,604 combined pill users compared with 3,466 women not taking medication, gamma-GT was higher with only 4 of the 11 estrogen-progestin combinations studied.
A moderately raised gamma-GT on the pill therefore deserves to have that information on the table, alongside the usual causes such as alcohol and other medicines. It does not rule out a liver problem, so your doctor decides what comes next.
Lipid panel on the pill: triglycerides, HDL and LDL
The effects on lipids are real and vary with the formulation. A 1990 study of 1,060 pill users and 418 women not on the pill measured a rise in fasting triglycerides of 13 to 75% depending on the pill used, with no increase in total cholesterol. The effects on HDL and LDL differ from one progestin to another. Those formulations were studied decades ago: the 1998 study above, with more recent pills, found triglycerides 8.5 to 36% higher.
High CRP on the pill
This marker of inflammation also rises on combined birth control, by an amount that varies with the formulation. A slightly raised CRP with no sign of infection therefore deserves to be read with that information in mind.
Key point - Total cortisol, total T4 and T3, testosterone, triglycerides, CRP and sometimes gamma-GT can be changed by combined birth control. In several cases, it is the measurement that changes, not your biological balance.
Your report knows nothing about your birth control, your treatments or your situation. BioSense does, if you tell it. Import your blood test, fill in your context, and receive a plain-language reading of each biomarker that takes it into account. Your data is hosted on servers located in France.
[→ Import my blood test](/en/onboarding/upload)
Patch and vaginal ring: similar effects on blood tests
One might think that the patch or the vaginal ring, which do not go through the digestive tract first, spare the liver. They do not.
Comparative studies show it: SHBG was higher with the patch and the ring than with a levonorgestrel pill. The effects described above can therefore also apply to these two forms, sometimes more markedly.
Progestin-only methods contain no estrogen, so this estrogen-driven rise in transport proteins is not the mechanism at work. It is still worth reporting them.
The practical conclusion remains the same: state precisely which method you use and in what form, rather than simply saying that you are on birth control.
Do you need blood work before starting birth control? What the CDC says
In the US, the reference is the CDC's U.S. Selected Practice Recommendations for Contraceptive Use (2024), read with the U.S. Medical Eligibility Criteria (2024). For combined hormonal contraceptives in people presumed to be healthy:
- Blood pressure is Class A, meaning essential before starting.
- Lab tests are Class C, meaning they do not contribute substantially to safe and effective use. This covers lipids, liver enzymes, glucose, hemoglobin and thrombophilia testing.
- Weight is not needed to determine eligibility.
So a healthy person does not need a lipid panel or a glucose test just to start the pill, patch or ring. The same applies to follow-up: the CDC says no routine follow-up visit is required, while monitoring blood pressure remains important at routine visits.
These recommendations do not replace individual care. Known conditions such as high blood pressure, migraine, a history of blood clots, diabetes or a lipid disorder are assessed with the eligibility criteria, and your doctor may then order specific tests.
Blood work may also be useful for reasons other than contraception. That framework belongs to your doctor or nurse practitioner, and it cannot be replaced by a personal reading of the results.
Key point - According to the CDC, blood pressure is the check that matters before starting combined birth control. Routine lab tests are not needed in healthy people, though your history may change that.
Why to report birth control before a blood test
Birth control is among the pieces of information most often left out when people talk about their treatments.
Reporting it avoids two symmetrical pitfalls.
The first is unnecessary testing. A raised cortisol, a gamma-GT above the range or an abnormal total T4 can trigger further tests that may not have been needed if the information had been available from the outset.
The second is needless worry while waiting for the appointment.
The BioSense method
A lab report knows nothing about your treatments or your lifestyle. BioSense asks you for those elements, sets each biomarker against what you have told it and follows its trend from one test to the next.
*ChatGPT answers you. BioSense knows you.* *BioSense, your prevention companion.* BioSense does not provide a diagnosis and does not replace your doctor. It is a prevention companion that helps you understand, ask the right questions and act day to day.
Birth control and blood tests: three questions to ask your doctor
If you are on birth control and a result raises a question for you, these three questions frame the appointment:
- Can this result be explained by my birth control, or should we look elsewhere?
- For this marker, is there a test less influenced by my birth control, for example a free fraction rather than a total value?
- Given my personal and family history, do I need any specific monitoring, and how often?
Frequently asked questions
Does birth control affect blood test results?
Yes, the combined pill can change some results without any disorder being present. This applies to total cortisol, total T4 and T3, testosterone, triglycerides, CRP and, with some formulations, gamma-GT. In a 2011 randomized trial, however, TSH and free T4 did not change in any relevant way.
Does birth control raise cholesterol?
The pill mainly changes triglycerides, and has less effect on total cholesterol. In a 1990 study of more than a thousand users, total cholesterol did not rise, while triglycerides rose by 13 to 75% depending on the formulation. The effect on HDL and LDL depends on the progestin.
Should I stop the pill before a blood test?
No, not on your own: simply tell the lab and your doctor about your birth control. Only a specific workup, such as looking for excess cortisol, may lead to discussing a temporary stop. That decision rests with your doctor.
What tests do you need before starting birth control?
For healthy people, the CDC (2024) lists blood pressure as the only essential check before starting combined birth control. Lab tests such as lipids, glucose and liver enzymes are not routinely needed. Your doctor may order them based on your history.
*This article is strictly informational and constitutes neither medical advice nor a diagnosis. For any question about your health or your birth control, consult your doctor.*
Import your blood test and receive a plain-language reading of each of your biomarkers, set in the context of your personal situation and followed from one test to the next. Your data is hosted on servers located in France.
[→ Import my blood test](/en/onboarding/upload)
Sources and methodology
International
- Fleseriu M, Auchus R, Bancos I, et al. Consensus on diagnosis and management of Cushing's disease: a guideline update. Lancet Diabetes & Endocrinology, 2021;9(12):847-875. PMC
- Zimmerman Y, Eijkemans MJC, Coelingh Bennink HJT, et al. The effect of combined oral contraception on testosterone levels in healthy women: a systematic review and meta-analysis. Human Reproduction Update, 2014;20(1):76-105. PMC
United States
- CDC. U.S. Selected Practice Recommendations for Contraceptive Use, 2024: Appendix C, Examinations and Tests Needed Before Initiation of Contraceptive Methods. CDC
- CDC. U.S. Selected Practice Recommendations for Contraceptive Use, 2024: Combined Hormonal Contraceptives. CDC
- Nguyen AT, Curtis KM, Tepper NK, et al. U.S. Medical Eligibility Criteria for Contraceptive Use, 2024. MMWR Recommendations and Reports, 2024;73(RR-4):1-126. CDC
- American Thyroid Association. Thyroid Function Tests. Patient information. ATA
- Endocrine Society. Nieman LK, et al. The Diagnosis of Cushing's Syndrome: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2008;93(5):1526-1540. PMC
- MedlinePlus, National Library of Medicine. Cortisol blood test. MedlinePlus
- Jensen JT, Burke AE, Barnhart KT, et al. Effects of switching from oral to transdermal or transvaginal contraception on markers of thrombosis. Contraception, 2008;78(6):451-458. PMC
United Kingdom
- Godsland IF, Crook D, Simpson R, et al. The effects of different formulations of oral contraceptive agents on lipid and carbohydrate metabolism. New England Journal of Medicine, 1990;323(20):1375-1381. PubMed
Europe
- Ågren UM, Anttila M, Mäenpää-Liukko K, et al. Effects of a monophasic combined oral contraceptive containing nomegestrol acetate and 17β-estradiol in comparison to one containing levonorgestrel and ethinylestradiol on markers of endocrine function. European Journal of Contraception and Reproductive Health Care, 2011;16(6):458-467. PMC
- Ågren UM, Anttila M, Mäenpää-Liukko K, et al. Effects of a monophasic combined oral contraceptive containing nomegestrol acetate and 17β-estradiol compared with one containing levonorgestrel and ethinylestradiol on hemostasis, lipids and carbohydrate metabolism. European Journal of Contraception and Reproductive Health Care, 2011;16(6):444-457. PMC
- Schiele F, Vincent-Viry M, Fournier B, et al. Biological effects of eleven combined oral contraceptives on serum triglycerides, gamma-glutamyltransferase, alkaline phosphatase, bilirubin and other biochemical variables. Clinical Chemistry and Laboratory Medicine, 1998;36(11):871-878. PubMed
- Fleischer K, van Vliet HA, Rosendaal FR, et al. Effects of the contraceptive patch, the vaginal ring and an oral contraceptive on APC resistance and SHBG: a cross-over study. Thrombosis Research, 2009;123(3):429-435. PubMed
*Methodological note: this article describes documented changes in test results. It passes no judgment on the choice of a birth control method, a question that belongs to a discussion with your doctor and that involves considerations far wider than the reading of a blood test.*
*BioSense methodology: our content is based on guidance from US authorities and medical societies (such as the USPSTF, CDC, NIH, FDA, ACC/AHA and ADA), UK bodies (NICE, NHS), European societies and the WHO. Sources are listed by country, and differences between countries are stated when they matter.*