Hormonal contraception: which blood tests to have before and during use

Hormonal contraceptives (pills, patches, vaginal rings, injections, implants and hormonal coils) are among the most thoroughly studied groups of medicines. This does not mean they have no effect on the body: oestrogens and progestogens affect blood clotting, the liver, lipid and carbohydrate metabolism, and blood pressure. It is therefore worth having several blood tests both before starting and during use. Below, we explain which tests matter, why, and how often to repeat them. Your gynaecologist decides on the contraceptive method; the tests help ensure it is safe.

Why tests before starting contraception matter

The greatest risk associated with preparations containing oestrogen is venous thromboembolism. It is rare, but the risk increases several-fold in women with inherited thrombophilia, those who smoke after the age of 35, and those with obesity or migraine with aura. Some of these factors are identified through your medical history, others only through blood tests. The second area is the liver, which metabolises hormones; the third is lipid metabolism and glucose, because oestrogens raise triglycerides and progestogens may reduce insulin sensitivity.

Tests before starting contraception

Full blood count

A basic screening test: it rules out anaemia (common with heavy periods) and platelet disorders, which affect blood clotting.

Liver function tests: ALAT, ASPAT, GGT, bilirubin

Active liver disease is a contraindication to oestrogen-containing contraception. Normal liver function tests before starting provide a baseline for later checks.

Lipid profile and glucose

Total cholesterol, LDL, HDL, triglycerides and fasting glucose. High triglycerides or abnormal blood glucose do not rule out contraception, but they affect the choice of preparation (e.g. methods without oestrogen) and how often checks are needed.

Blood clotting

Standard tests: activated partial thromboplastin time (APTT), PT (INR), fibrinogen and, potentially, D-dimer. A full thrombophilia work-up (factor V Leiden mutation, prothrombin gene mutation, protein C, protein S, antithrombin and antiphospholipid antibodies) is not recommended for every woman, but makes sense if there is a family history of thrombosis, pulmonary embolism, strokes at a young age or recurrent miscarriages. It is worth discussing these tests with your doctor before having them, as their interpretation is complex.

Thyroid-stimulating hormone (TSH)

Thyroid disorders are common in women and affect the menstrual cycle as well as body weight and mood; these symptoms can easily be mistaken for “side effects of the pill”. Testing TSH before starting contraception helps avoid incorrect conclusions.

Prolactin

Oestrogens can slightly raise prolactin levels. A baseline result makes assessment easier if you develop milky nipple discharge, headaches or visual disturbances during use.

Blood pressure and BMI

These are not blood tests, but they are part of standard assessment: blood pressure above 140/90 mmHg and a BMI above 30 change the balance of benefits and risks of combined contraceptives.

Tests during use

It is worth repeating liver function tests and a lipid profile 3–6 months after starting, then checking them once a year, together with a full blood count, glucose and blood pressure. For women with risk factors (being overweight, smoking or a family history of diabetes), the doctor may recommend more frequent checks and additional HbA1c or fasting insulin tests. Annual cervical screening and a gynaecological examination remain separate from blood tests.

How contraception affects test results

This is important when interpreting results of tests performed for other reasons. Oestrogens increase levels of hormone-binding proteins, so TSH may be slightly different, while total thyroxine (T4) and total cortisol are raised despite normal free hormone fractions. SHBG increases, which lowers free testosterone (this is why the pill improves acne). FSH, LH and oestradiol do not reflect the activity of your own ovaries: measuring them while using contraception serves no purpose unless your doctor advises otherwise. CRP, fibrinogen and triglycerides also increase; vitamin B12 and folate (folic acid) decrease slightly. The doctor interpreting the result should know that you are using hormones.

Symptoms that require immediate medical attention

• pain and swelling in one calf, sudden breathlessness, chest pain (suspected thrombosis or embolism),
• a severe, new headache, visual or speech disturbances, numbness on one side of the body,
• jaundice, dark urine, pain under the right rib cage,
• a sudden rise in blood pressure.

Preparing for the tests

Have the tests in the morning, on an empty stomach (12 hours without food; water is allowed), after a night’s rest. Take your contraceptive pill as usual. Before a lipid profile and glucose test, avoid alcohol for 2–3 days and unusually fatty meals the day before. Blood for prolactin testing is collected after 30 minutes of quiet rest. For coagulation tests, you need to report any medicines you take, including aspirin and anti-inflammatory medicines.

Frequently asked questions

Do I need clotting tests before starting the pill?

Basic coagulation tests are sensible; a full thrombophilia work-up is only needed if there is a relevant family or personal medical history. Your gynaecologist decides.

How often should liver function be checked while using contraception?

3–6 months after starting, then once a year, unless results or symptoms indicate a need for more frequent checks.

Can I have these tests without a referral?

Yes. A full blood count, liver function tests, lipid profile, glucose, TSH, prolactin and coagulation tests are available privately; you can show the dated results to your doctor at your appointment.

Sources

• Drosdzol-Cop A. et al., Ginekologia i Perinatologia Praktyczna, Rekomendacje PTGiP dotyczące wskazań i bezpieczeństwa stosowania preparatów antykoncepcyjnych (PTGiP [Polskie Towarzystwo Ginekologów i Położników — Polish Society of Gynaecologists and Obstetricians] recommendations on the indications and safety of contraceptive preparations), 2025. journals.viamedica.pl
• WHO, Medical Eligibility Criteria for Contraceptive Use, 5th ed., 2015. who.int
• CDC, MMWR, U.S. Medical Eligibility Criteria for Contraceptive Use, 2024, 2024. cdc.gov