Many women who have just received their hormone test results fixate on a single line: the LH to FSH ratio. They read online that a “2 to 1” ratio signals PCOS, then panic when their number looks high, or feel confused when it comes back normal despite obvious symptoms. The reality is more nuanced. The LH/FSH ratio can offer a clue, but it is not one of the three official features used to confirm PCOS. This article explains what the number actually means, when it is useful, and why you should never rely on it alone.
What LH, FSH, and their ratio actually are
LH (luteinising hormone) and FSH (follicle-stimulating hormone) are two hormones released by the pituitary gland in the brain. Both control the ovaries: FSH helps follicles grow and mature, while LH triggers ovulation and stimulates androgen production. In a normal menstrual cycle these two hormones rise and fall rhythmically, and in the early part of the cycle (the follicular phase) their levels are roughly balanced.
The LH/FSH ratio is simply the LH level divided by the FSH level. In women without PCOS this ratio usually sits close to 1 to 1 in the early cycle. In some women with PCOS, LH tends to run higher than FSH, producing a ratio such as 2 to 1 or sometimes 3 to 1. This is where the widely shared “rule of thumb” comes from, but as we will see, the number is far from conclusive.
Why LH can rise in PCOS
The main reason lies in how the brain signals the ovaries. The pituitary is driven by pulses of GnRH from the hypothalamus. In PCOS these GnRH pulses become faster and more frequent, which preferentially pushes the pituitary to release more LH than FSH. The result is a higher LH level, a flat or modest FSH, and therefore a raised ratio. This excess LH also stimulates the ovaries to make more androgens, which explains the link between a high LH/FSH ratio and androgen signs such as stubborn acne or hirsutism.
However, one important factor changes the picture: body weight and insulin resistance. Women with PCOS who carry more weight tend to have a lower LH/FSH ratio, because excess fat tissue and high insulin blunt LH secretion. Lean PCOS, by contrast, more often shows a high ratio. Current estimates suggest that roughly one third to one half of women with PCOS actually have a normal body weight, and it is in this group that a high ratio appears most often. Since the majority of women seen in our clinics carry excess weight or have insulin resistance, many of them have a “normal”-looking LH/FSH ratio even though they clearly have the condition. This is the core reason a single number cannot be the deciding factor.
Why it is not a diagnostic criterion
This is the most important point to grasp. The 2023 international PCOS guideline and the Rotterdam criteria do not include the LH/FSH ratio as a diagnostic requirement. PCOS is confirmed through the Rotterdam criteria, namely two of three features: irregular periods, signs of high androgens, and polycystic ovaries on ultrasound or a high AMH level. The LH/FSH ratio is nowhere on that list.
The reason is simple, and the evidence here is strong: the test is not precise enough to stand on its own. Studies going back years show that many women who meet PCOS criteria in every other respect still have normal LH, FSH, and ratio values. In other words, a normal ratio does not rule PCOS out, and a high ratio does not confirm it in isolation. The international expert panel that revised the guideline in 2023 stated specifically that gonadotrophin measurements, namely LH and FSH, are no longer part of the diagnostic criteria. This is exactly why doctors in Malaysia, who follow the same international guideline, do not use the ratio as a deciding test. Instead it is sometimes checked as supporting information, or more often FSH is measured to help exclude other causes such as ovarian failure.
Understanding the numbers and units on your report
When you are holding a lab slip, LH and FSH are usually reported in IU/L (international units per litre). The ratio is not a separate test; it is simply the figure you get by dividing the two numbers. So if your slip does not print a ratio, you can work it out yourself by dividing the LH value by the FSH value. For example, an LH of 12 IU/L and an FSH of 6 IU/L gives a ratio of 2 to 1.
What matters to understand is that different laboratories use different kits and reference ranges, so the “normal” figures are not uniform everywhere. More importantly, LH is secreted in pulses throughout the day, rising and falling within minutes. A single blood draw captures only one moment in that rhythm, so the reported value can look high or low purely because of when it was taken. This is the technical reason a single LH/FSH reading cannot be treated as final, and why doctors trust the overall clinical picture more than one number.
When the test is genuinely useful
Although it is not a criterion, LH and FSH still have their place. Measuring FSH is valuable for ruling out conditions that mimic PCOS, especially when periods have stopped. A very high FSH, for example, points to a declining ovarian reserve or early menopause rather than PCOS. FSH and LH that are both low may instead signal a problem at the pituitary or hypothalamic level, such as amenorrhoea from stress, excessive exercise, or very low body weight. In cases like these, the pattern of LH and FSH helps the doctor steer the diagnosis in the right direction.
A high LH/FSH ratio can also lend support to the overall picture in a lean woman whose symptoms are subtle, by hinting that a neuroendocrine disturbance is present. But again, it supports rather than confirms. Doctors always read this number alongside symptoms, physical examination, and other tests such as testosterone, AMH, and ultrasound, never in isolation.
Timing of the test changes the result
A common reason LH/FSH results are misread is blood drawn at the wrong time. To mean anything, this test should be done in the early cycle, on day 2 to 5 after a period begins. Around mid-cycle, LH surges naturally as part of ovulation, so a sample taken then will show a falsely high, meaningless ratio.
The challenge is that many women with PCOS have such irregular periods that knowing when the “early cycle” actually is becomes difficult. This is yet another reason the ratio is less reliable in PCOS than in other conditions. If you are taking the contraceptive pill or any hormonal therapy, LH/FSH results also cannot be interpreted, because those medications suppress both hormones. The same applies if you stopped the pill only in the last few months, as the hormonal axis may not have fully recovered. Tell your doctor about every medication you take, including supplements and fertility drugs, so the results are not misread.
Questions worth asking your doctor
When you see your doctor with results in hand, a few simple questions can make the visit far more useful. You can ask: “On which cycle day was this blood drawn, and was the timing appropriate?” This matters because it determines whether the ratio can be trusted at all. You can also ask: “Does this result change my diagnosis, or is it just supporting information?” That helps you understand the true weight of the number. A useful third question is: “Which other tests matter more for my case?” For most women the answer is testosterone, fasting glucose or HbA1c, and a lipid profile, because these are the tests that guide treatment and long-term monitoring.
What to do with the number
If you are holding a result and see an LH/FSH ratio, resist the urge to draw your own conclusions. A high number does not mean your case is “more severe”, and a normal number does not mean you do not have PCOS. Bring the full result, together with your symptom list and period dates, to a gynaecologist or endocrinologist. They will weigh the whole picture, not a single line.
You can begin this process at a KKM Klinik Kesihatan for around RM1 per visit for citizens, basic investigations included, before being referred to a specialist clinic if needed. A follow-up visit is usually around RM5. Private clinics offer shorter waiting times but their costs vary by location, so confirm first. Whichever path you choose, remember that a PCOS diagnosis opens the door to important long-term monitoring: many Malaysian women do not realise that PCOS raises the future risk of type 2 diabetes and heart disease. Keeping an eye on your blood sugar and blood pressure over time matters far more for your health than worrying about a single hormone ratio.
To understand the condition as a whole, start with what is PCOS. If you have just been diagnosed and are wondering what comes next, the newly diagnosed PCOS guide lays out your first-week steps in order, including the questions you should ask your doctor about your test results.