Perimenopause and blood tests: what they can and cannot show

Hot flushes, poor sleep, low mood, brain fog and changing periods lead many women in their 40s to ask for a blood test to confirm perimenopause. It is a reasonable request, but the answer surprises people. For most women, a hormone test cannot confirm or rule out perimenopause. Blood tests are useful here, just not in the way many expect.

What perimenopause is

Perimenopause is the transition before your final period. It usually starts in the mid 40s and can last several years. Menopause itself is defined in hindsight, once you have gone 12 months without a period. During the transition the ovaries do not shut down smoothly. They sputter, with some cycles almost normal and others very different.

Why FSH is not a reliable test

As the ovaries wind down, FSH tends to rise. The problem is that in perimenopause it rises and falls unpredictably. A high FSH one month can be followed by a normal level the next, and oestradiol can swing from very low to higher than usual. A single result catches one moment in that storm and can easily mislead in either direction.

For this reason, the UK's National Institute for Health and Care Excellence (NICE) menopause guideline advises that women over 45 with typical symptoms can be diagnosed with perimenopause or menopause without any blood test. It specifically advises against using FSH, oestradiol, AMH and several other tests to diagnose it in that age group.

Hormonal contraception adds another layer. On the combined pill and some other methods, FSH is suppressed and tells you nothing about the ovaries. Many women in their 40s use contraception, which is one more reason symptoms and history usually count for more than a number.

What blood tests can show

Several common conditions cause symptoms that overlap with perimenopause. A blood test is a good way to check for them, so you are not putting everything down to hormones when something else is treatable.

• Thyroid. An underactive or overactive thyroid can cause tiredness, weight change, low mood, feeling hot or cold and changes to periods. The Well Woman panel includes TSH and TPO antibodies, and thyroid problems become more common in midlife.
• Iron and anaemia. Periods often become heavier and closer together in perimenopause, which can drain iron. Low ferritin or haemoglobin causes fatigue, poor concentration and breathlessness.
• Blood sugar. Rising HbA1c or fasting glucose can cause tiredness and is worth knowing about as metabolism shifts.
• Vitamin D. Low levels matter more as bone loss speeds up around menopause.

The health changes worth tracking

Oestrogen helps protect the heart and bones. As it falls, LDL cholesterol often rises, and bone density drops fastest in the years around the final period. Your cholesterol results, blood sugar and kidney and liver markers give a baseline for this new phase of life.

LifePrint uses the SA Heart and LASSA 2018 dyslipidaemia guideline for cholesterol, which sets an LDL target below 3.0 mmol/L for people at low to moderate risk. Results from 3.0 to 3.4 mmol/L appear in your report's grey zone. A result that was fine at 40 and is climbing at 48 is exactly the kind of trend worth discussing with a doctor.

What about AMH?

AMH, an add-on to the Well Woman panel, falls as the number of remaining eggs declines. A very low AMH is consistent with the late stages of the transition, but it cannot tell an individual woman when her final period will be, and NICE does not recommend it for diagnosing perimenopause in women over 45. It is most useful for fertility questions, which we cover in a separate article.

Talking to a doctor

If your symptoms are affecting your life, see a doctor even if your blood tests look normal. Normal results do not mean the symptoms are imaginary, and there are many ways to help, from lifestyle changes to treatment. Decisions about hormone therapy depend on your personal history and risks, and belong in that conversation. Bring your LifePrint report so your doctor can see what has already been checked.

Keep a simple record of your periods and symptoms for a few months before the appointment. It is often more useful than any single blood result.