Polycystic Ovary Syndrome Blood Test Kit

Follicle Stimulating Hormone is produced by the pituitary gland in the brain and is essential for reproductive function. In women, FSH stimulates the growth and maturation of ovarian follicles—the fluid-filled sacs in the ovaries that each contain an egg. During the first half of the menstrual cycle (follicular phase), FSH levels rise to promote follicle development. One follicle becomes dominant and continues to mature, while the others regress. After ovulation, FSH levels decline. Normal early follicular phase FSH is typically 3-10 IU/L. In PCOS, FSH is often normal or low-normal, which contrasts with LH (which is often elevated). The relationship between FSH and LH is more informative than either hormone alone. In women with regular ovulatory cycles, the FSH: LH ratio is approximately 1:1 in the early follicular phase. In PCOS, this ratio is often reversed, with LH being 2-3 times higher than FSH (LH: FSH ratio >2:1 or even >3:1). However, not all women with PCOS have this altered ratio. FSH also provides information about ovarian reserve and menopausal status. Elevated FSH (particularly above 10-15 IU/L) can indicate diminished ovarian reserve or perimenopause, where the ovaries are becoming less responsive and the pituitary produces more FSH to try to stimulate them. This is important to distinguish from PCOS, which typically shows normal or low FSH. Results outside the normal range may need a follow-up with your GP.

Luteinising Hormone is produced by the pituitary gland alongside FSH and is critical for ovulation. In women, LH triggers ovulation—the release of a mature egg from the ovary—by causing the dominant follicle to rupture. After ovulation, LH helps form the corpus luteum, which produces progesterone to support early pregnancy. LH levels are relatively low in the early follicular phase (typically 2-15 IU/L), surge dramatically mid-cycle to trigger ovulation (reaching 20-100+ IU/L), then decline in the luteal phase. In PCOS, LH is often elevated relative to FSH, even in the early follicular phase. This reversed LH: FSH ratio (typically >2:1) is a classic biochemical feature of PCOS, though it's not present in all cases. The elevated LH stimulates the ovarian theca cells to produce excess androgens (testosterone and its precursors), contributing to the hyperandrogenism that causes acne, hirsutism, and other symptoms. High LH also disrupts normal follicle development—follicles begin to develop but fail to mature properly, leading to multiple small follicles (the "polycystic" appearance on ultrasound) and irregular or absent ovulation. It's important to note that LH pulses throughout the day, so a single measurement provides a snapshot. The LH: FSH ratio is most meaningful when measured in the early follicular phase (days 2-5). If measured at other times, particularly near the mid-cycle surge, interpretation is difficult. Results outside the normal range may need a follow-up with your GP.

Testosterone is the primary androgen (male hormone), though women also produce it in smaller amounts in the ovaries and adrenal glands. In women, normal testosterone levels are approximately 0.5-2.5 nmol/L—much lower than in men. Testosterone is responsible for libido, energy, muscle maintenance, and has effects on mood and cognition. However, excess testosterone causes masculinising effects: acne, oily skin, excess facial and body hair (hirsutism), scalp hair thinning in a male pattern, and deeper voice. Elevated testosterone is one of the key biochemical features of PCOS. The excess androgens come primarily from the ovaries, driven by elevated LH stimulating theca cells. Some women with PCOS have clearly elevated total testosterone; others have testosterone in the "normal" range but elevated free testosterone (because SHBG is low, leaving more testosterone unbound and active). This is why measuring SHBG and calculating the Free Androgen Index is important—total testosterone alone can miss hyperandrogenism in some women. Very high testosterone (above 5 nmol/L in women) raises concern about other causes such as androgen-secreting tumours of the ovary or adrenal gland, which require urgent investigation. Moderate elevation is more typical of PCOS. Testosterone should be measured in the morning when levels are highest, and ideally in the early follicular phase of the cycle for consistency. Results outside the normal range may need a follow-up with your GP.

The Free Androgen Index is a calculated marker that estimates the proportion of testosterone that is biologically active (free and able to act on tissues). It's calculated using the formula: FAI = (Total Testosterone ÷ SHBG) × 100. Most testosterone in the blood is bound to proteins—primarily SHBG and albumin—and only the small "free" fraction (about 1-3%) can enter cells and exert androgenic effects. The FAI provides a better reflection of androgen status than total testosterone alone, particularly in conditions where SHBG is altered. In PCOS, the FAI is often elevated even when total testosterone appears normal. This occurs because SHBG is frequently low in PCOS (related to insulin resistance and elevated androgens, which both suppress SHBG production). With less SHBG to bind testosterone, a greater proportion remains free and active, causing symptoms of androgen excess. A woman with "normal" total testosterone but low SHBG may have significantly elevated FAI and clinical hyperandrogenism. Normal FAI in women is typically below 5 (though reference ranges vary by laboratory). Values above 5-7 suggest hyperandrogenism. FAI is considered one of the more sensitive markers for detecting androgen excess in women and is particularly useful in PCOS investigation. However, FAI should always be interpreted alongside the actual testosterone and SHBG values, as the same FAI can result from different combinations of these markers. Results outside the normal range may need a follow-up with your GP.

Sex Hormone Binding Globulin is a protein produced primarily by the liver that binds and transports sex hormones—testosterone, dihydrotestosterone (DHT), and oestradiol—in the bloodstream. Hormones bound to SHBG are inactive; they cannot enter cells or exert effects. SHBG therefore acts as a buffer, regulating how much active hormone is available to tissues at any given time. Normal SHBG in women is typically 30-100 nmol/L, though it varies with age, weight, and hormonal status. SHBG production is suppressed by androgens and insulin, and increased by oestrogens and thyroid hormones. In PCOS, SHBG is often low due to the combination of elevated androgens (which suppress SHBG) and insulin resistance (hyperinsulinaemia also suppresses SHBG). This creates a vicious cycle: low SHBG means more free, active testosterone, which further suppresses SHBG and worsens androgen excess symptoms. This is why weight loss and insulin-sensitising treatments (like metformin) often help PCOS—they reduce insulin resistance, allowing SHBG to rise and free testosterone to fall. Low SHBG in a woman with PCOS symptoms is supportive evidence of the diagnosis and suggests metabolic involvement (insulin resistance). Very low SHBG (below 20-30 nmol/L) is associated with increased cardiovascular and metabolic risk. Conversely, high SHBG is seen with oestrogen excess (oral contraceptives, pregnancy), hyperthyroidism, anorexia, and liver disease. SHBG is essential for interpreting testosterone results and calculating the Free Androgen Index. Results outside the normal range may need a follow-up with your GP.