Demystifying PCOS and understanding the essential blood tests

September 12, 2023

In my last post about PCOS I discussed some of the signs and symptoms that accompany this relatively common condition. Today I want to look at the blood tests needed to help identify if it is PCOS or something else. But first, let us look at the normal menstrual cycle.

Normal menstrual cycle

Once a month, the brain (including the pituitary gland), ovaries, and uterus go through a series of events that help prepare the body for pregnancy. The pituitary gland produces two hormones: follicle-stimulating hormone (FSH) and LH. The ovaries also produce two more hormones, progesterone, and oestrogen.

Small increases in FSH stimulate the ovary to form a follicle containing an egg (oocyte) during the first part of the cycle. The follicle produces increasing amounts of oestrogen, which causes the uterine lining to thicken and the pituitary to release a large amount of LH. This midcycle "surge" of LH enables the egg to be released from the ovary (known as ovulation) 36 to 48 hours after the LH surge. If the egg is fertilised by a sperm, it develops into an embryo that travels to the uterus via the fallopian tube. The ovary generates both oestrogen and progesterone after ovulation, which prepares the uterus for probable embryo implantation and pregnancy.

Menstrual cycle in PCOS

Multiple tiny follicles (small cysts 4 to 9 mm in diameter) accumulate in the ovary of women with PCOS. None of these little follicles/cysts are capable of developing large enough to cause ovulation. As a result, oestrogen, progesterone, LH, and FSH levels become skewed.

Diagnosis of PCOS is difficult.

There is no single test that can identify PCOS, therefore the focus is on family history, symptoms, and signs. A physical exam may be required to look for additional body hair, acne, male-pattern baldness, and skin discolouration. Waist circumference can be measured to determine BMI. This may be followed  by a pelvic ultrasound to see if the ovaries are actually polycystic or if there is a thickened uterine lining. 

Blood tests are also important in helping to identify PCOS. They include testing for the levels of FSH, LH, Androgens, and Prolactin

FSH (Follicle stimulating hormone) 

Follicle-stimulating hormone (FSH) is linked to human sexual development and functioning. FSH levels differ depending on gender and age and it works differently at various ages. For example, it helps the ovaries create oestrogen in young girls and the testes produce testosterone in young boys.

FSH aids in the regulation of the reproductive system. FSH levels in women increase egg growth and release, while FSH levels in males regulate sperm production.

FSH interacts with luteinizing hormones (LH) to regulate sexual activities, so both tests are frequently performed concurrently.

The pituitary gland produces FSH, and an FSH test is important if you have pituitary gland issues, which might include tiredness, weight loss, and decreased appetite. Other pituitary-related disorders include infertility, difficulty conceiving, abnormal menstrual cycles, menopause, or perimenopause. This test is usually administered during the first week of the cycle, with day 1 being the first day of a period.


A low FSH result may indicate the possibility of the following: being underweight, a dysfunction of the pituitary gland, and the ovaries not producing sufficient eggs. 

A high FSH result may indicate the possibility of the following:  an ovarian tumour, premature ovarian failure, PCOS, menopause, or Turner syndrome.

Interpreting FSH blood test results has to take age and existing health issues into consideration.

Luteinizing hormones (LH)

Luteinizing hormone is one of the body's most important hormones. It is produced by the pituitary gland, which is located at the base of the brain, near the front of the skull. This hormone sends messages from the brain to the reproductive organs so as to stimulate a variety of human body processes, including development, sexual health, and reproduction.

The pituitary gland produces and releases LH once it receives a signal from the hypothalamus to do so. If the hypothalamus detects that there is insufficient LH in your body, it will begin the process of producing more. If it detects that you have enough LH, it will stop producing it. LH works in conjunction with follicle-stimulating hormone (FSH) to control the menstrual cycle which includes the release of an egg from an ovary each month (ovulation).

LH levels rise and fall, based on where you are in your menstrual cycle. This hormone triggers the ovary to release eggs, a process called ovulation and “surges” to its highest point just before ovulation occurs.

 Once an egg has been released, the corpus luteum, (a temporary structure within the ovary) generates progesterone and disintegrates if pregnancy does not occur. If a pregnancy occurs, other hormones take over the duty of maintaining progesterone levels, and LH levels fall.

  • A small amount of LH, like all hormones, can have a significant impact on how the body functions. Too much or too little LH might can skew this communication loop, resulting in certain medical concerns. Too much LH may indicate,
  •  Primary ovarian failure 
  • PCOS 

Low levels of the luteinizing hormone may indicate,

  • Secondary ovarian failure.

For a woman of reproductive age and not pregnant or using contraceptives the level of LH depends on the point in the cycle with the following indicating a normal range.

  • The follicular phase: 1.9 to 12.5 IU/L
  • Ovulatory phase: 8.7 to 76.3 IU/L
  • The luteal phase: 0.5 to 16.9 IU/L

The normal levels of LH and FSH are in the range of 4-8 during reproductive age in women, and the LH: FSH ratio is 1. However, in women with PCOS, this ratio may be as high as 2:1 or even 3:1. But the LH:FSH ratio may be normal in women with established diagnoses of PCOS as can FSH levels. Usually, the LH levels will be raised to 10-20. This means the blood results of FSH and LH  levels do not necessarily confirm the presence of  PCOS but are still useful to establish fertility. FSH and LH each need to be present at certain levels and at specific times during the normal menstrual cycle for proper follicle and egg development to ensue. 

An imbalance between   LH and FSH   can also stimulate the secretion of testosterone and other androgens and androgens include testosterone and dehydroepiandrosterone (DHEA).

Total Testosterone and Free Testosterone

Testosterone is made by:

  • The testicles (or testes), are the part of the male reproductive system that makes sperm.
  • The ovaries, the part of the female reproductive system that makes eggs.
  • The adrenal glands, are organs on top of each kidney that make several hormones. 

Normally, the testosterone level is very low in females as compared to males. Elevated levels of testosterone may lead to symptoms such as abnormal facial and body hair, and acne in women with PCOS.

Total testosterone is the total amount of testosterone in your body, which includes free testosterone. Free testosterone is only a small fraction of testosterone that is actually active and available in the body. The normal total testosterone level in females of reproductive age is 15-70 ng/dL, whereas the normal free testosterone level in females is 0.7-3.6 pg./mL. 

Raised levels of both total and free testosterone are frequently seen in women with PCOS.

These various kinds of testosterone are measured using three distinct types of blood tests:

• A total testosterone test detects free testosterone as well as testosterone bound to proteins. This is the most common sort of examination.

• A free testosterone test only detects "active" testosterone. Although this test is less prevalent, it may be effective in diagnosing some medical disorders.

• A bioavailable testosterone test measures free testosterone as well as testosterone that is weakly bound to albumin, a blood protein. This test is not routinely performed. However, it, like a free testosterone test, may aid in the diagnosis of certain medical issues.

DHEA-S (Dehydroepiandrosterone)

DHEA-S is another male hormone that is found in small quantities in females, usually in the range of 35-430 ug/dL. Several women with PCOS have a DHEA-S level of more than 200 ug/dL.

Finally, there are a few other medical conditions that produce symptoms comparable to PCOS, so prolactin levels and thyroid hormones are usually evaluated also. 

Prolactin: A higher-than-normal amount of prolactin can promote menstrual cycle irregularity, as seen in females with PCOS. The pituitary gland secretes the hormone prolactin. Prolactin levels in some PCOS women may be elevated. If you have high prolactin levels, an MRI of the pituitary gland may be performed to rule out a pituitary tumour.

TSH (thyroid stimulating hormone)

The thyroid gland produces TSH (thyroid stimulating hormone). Menstrual abnormalities and problems conceiving might be caused by thyroid underproduction or hyperthyroidism. Though TSH levels in PCOS are normally normal, this test may be performed as part of the PCOS blood test to rule out any thyroid issues.

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