PCOS and blood tests: the values that bring clarity

PCOS is common, and the blood values are half the investigation

PCOS (polycystic ovary syndrome) is one of the most common hormonal disturbances in women of fertile age; roughly one in ten is affected. Suspicion is often raised by infrequent or irregular periods, acne, increased hair growth, or a pregnancy that takes longer than expected. The symptoms arrive gradually and are shared with several other conditions, which is exactly why blood values play such a central role in the investigation.

The diagnosis rests, in Sweden as internationally, on the so called Rotterdam criteria: two out of three of infrequent or absent ovulation, elevated androgens showing clinically or in blood tests, and polycystic ovaries on ultrasound. Two of the three criteria can therefore be judged fully or partly from blood, while the third requires an ultrasound within care.

This guide walks through the values a PCOS investigation rests on: the androgens, the cycle hormones, the values that rule out what merely resembles PCOS, and the metabolic side. The goal is for you to understand what each value adds, and to arrive at a doctor's appointment with the right groundwork.

The androgens: testosterone, SHBG and the ratio between them

The core of the PCOS question is the androgens. The first value is total testosterone. In women the levels are normally low, and in PCOS they are usually mildly raised rather than dramatically high. A value within the reference range does not rule PCOS out, and a mildly raised value does not prove it, but the value is one of the cornerstones of an investigation and a requirement for judging the elevated androgen criterion.

The second value is SHBG (the protein that binds sex hormones in the blood). Only the portion of testosterone that is not tightly bound is biologically active. In PCOS, SHBG often runs low, partly linked to insulin resistance, and a low SHBG means a larger share of the testosterone is free and active. Two people with exactly the same total testosterone can therefore experience completely different real androgen effects.

This is why a free androgen index is calculated from testosterone and SHBG together. The index captures what a single total value misses, and in investigations it is often regarded as more sensitive than total testosterone for detecting biochemically elevated androgens in PCOS. It is the combination, not any single number, that answers the androgen question.

Sometimes DHEA-S is also measured, an androgen that comes mainly from the adrenal glands. It can help a doctor judge where an androgen excess is coming from, since the ovaries and the adrenals are two different sources with different follow up.

The cycle hormones: LH, FSH, estradiol and AMH

The cycle hormones complete the androgen picture. LH and FSH (the pituitary's two signal hormones to the ovaries) direct follicle maturation and ovulation. In PCOS, an LH that runs high relative to FSH is a common finding, a pattern that can contribute to ovulation failing to happen. The pattern is common but neither necessary nor sufficient for the diagnosis; entirely normal signal hormones do not rule PCOS out.

Estradiol (the body's main estrogen) is measured as part of the same picture. The value is often normal in PCOS, but it helps a doctor interpret the signal hormones and rule out other reasons the cycle has been disturbed.

AMH (anti-müllerian hormone) is made by the small egg follicles in the ovaries. In PCOS there are typically many small follicles, and AMH therefore often sits clearly higher than expected for age. International guidelines have in recent years opened for a clearly raised AMH in adults to be used, in some situations, as an alternative to ultrasound when judging the polycystic ovary criterion. A high AMH is thus a puzzle piece that strengthens the picture, not an answer in itself, and the interpretation belongs with a doctor.

The values that rule out look alikes: thyroid and prolactin

An important part of any serious investigation is looking for what merely resembles PCOS. Two conditions account for most of the confusion, and both show up in blood.

The first is the thyroid. Both an underactive and an overactive thyroid can disturb the cycle, affect weight and cause tiredness, and an underactive thyroid is common in women at the same ages when the PCOS question arises. TSH (the pituitary's signal to the thyroid) and free T4 (the active thyroid hormone) go a long way as a first check, and an abnormal result steers the investigation in an entirely different direction from PCOS.

The second is prolactin. A raised level can suppress ovulation and cause infrequent or absent periods, which is exactly the picture that raised suspicion in the first place. Prolactin is affected by stress, sleep and certain medicines among other things, so a mildly raised value is often repeated before conclusions are drawn.

Beyond this, a doctor may, given particular findings, want to rule out rarer causes such as congenital adrenal hyperplasia or cortisol disorders. Those investigations need other tests and belong within ordinary care. For most people, though, it is the androgens, the cycle hormones, the thyroid and prolactin that together make up the blood picture a PCOS investigation rests on, and that combination is what is worth bringing to a doctor's appointment.

If you want the core of the investigation measured in a single draw, testosterone, SHBG, the cycle hormones, the thyroid and prolactin are collected in Female Hormone Test Plus, taken without a referral whenever it suits you.

The metabolic side: blood sugar and blood fats

PCOS is not only a hormone question. A large share of those who receive the diagnosis also have insulin resistance, meaning the body's cells respond more sluggishly to insulin, and this includes many who are of normal weight. Insulin resistance is thought to be one of the drivers behind both the low SHBG levels and the androgen excess, and it is the reason PCOS is linked over time to a raised risk of type 2 diabetes.

So it makes sense for the metabolic side to be part of the picture early. HbA1c (long term blood sugar) shows the average blood sugar level over the past two to three months, and fasting glucose gives a snapshot. Fasting insulin, read together with glucose, can hint at insulin resistance, although that value is interpreted with some caution and is not used for diagnosis.

The blood fats belong here too. The pattern of raised triglycerides and low HDL cholesterol is common with insulin resistance and is worth knowing about early, because it can be influenced by habits and, when needed, treatment.

These are also the values where following them over time gives the most. Guidelines recommend that women with PCOS have their blood sugar picture checked regularly, and a baseline of your own, taken in good time, makes every later comparison more meaningful than any single measurement can be.

When to take the sample, and what to do with the results

Timing matters for some of the values. The cycle hormones LH, FSH and estradiol are best assessed in the early follicular phase, roughly day two to five counting from the first day of your period. If the cycle is very irregular, or periods are absent altogether, the sample can still be taken; the doctor then factors in that the cycle day is unknown. Androgens, SHBG, thyroid values and prolactin are less sensitive to cycle day.

Hormonal contraception is the most common source of error. Combined oral contraceptives raise SHBG sharply and suppress the androgens, which can mask exactly what the investigation is looking for. A fair androgen picture usually requires a pause of at least three months, but do not stop contraception solely for the sake of a test without weighing that decision first, ideally with a doctor.

When the results arrive, they are groundwork, not a verdict. Bring the values to a doctor if your periods have been infrequent or absent for several months, if hair growth or acne is increasing, if you are planning a pregnancy, or if any value sits clearly outside the reference range. A doctor can then place the values alongside your history, add an ultrasound if needed, and give a real answer to the question you started with.

Wherever the investigation leads, the values are not wasted. They are your baseline, and the next measurement will have something to be compared against.

This article is general health information, not medical advice and not an assessment of your values. If you have symptoms or concerns, contact your healthcare provider.