Hair loss in women: the blood tests worth doing first.

Blood tests will not explain every kind of hair loss, but four checkable causes come up again and again in women: low iron stores, thyroid dysfunction, raised androgens and low vitamin D. Ferritin, TSH and free T4, testosterone with SHBG, and vitamin D are the sensible first set.

Types of hair loss, and why a blood test only helps with some

Hair does not fall out in one way, and the pattern tells you a lot before a single tube of blood is collected.

• Telogen effluvium (diffuse shedding). Hair comes out all over, often by the handful in the shower, usually two to three months after a trigger: illness, surgery, a crash in weight, childbirth, or significant blood loss. This is the type most likely to have a blood-test answer, and the type most likely to recover once the cause is dealt with.
• Female pattern hair loss. Gradual thinning through the crown with a widening part, while the hairline stays. It is largely genetic and influenced by androgen sensitivity at the follicle, so bloods are often normal. Testing still matters here, because a coexisting iron or thyroid problem makes the thinning worse and is worth correcting.
• Alopecia areata. Smooth, well-defined round patches. This is autoimmune, diagnosed by a doctor on examination, not by a blood panel, though thyroid antibodies are sometimes checked alongside.
• Scarring alopecia. Loss of hair with redness, scaling, itching, burning or a shiny scalp where follicles have gone. This needs prompt assessment by a GP or dermatologist, because early review protects the hair that remains.
• Traction and breakage. Loss at the edges from tight styles, extensions or heat, or hair snapping mid-shaft. No blood test applies.

If you have patches, scalp pain, redness or scarring, start with a doctor's examination rather than a panel. For diffuse shedding and thinning, bloods earn their place.

Ferritin and hair: the level many doctors look for

Ferritin is the marker of your stored iron, and it is the one that matters for hair. You can have completely normal haemoglobin and a completely normal full blood count while your stores sit near empty, because your body protects red blood cells first and lets the stores go.

Below about 30 ug/L is widely used in Australia to indicate low iron stores, and some laboratories use 15. For hair, some clinicians look for a level comfortably above that lower limit, with figures around 50 to 70 ug/L commonly quoted; no Australian guideline sets a target for hair, the evidence linking a specific figure to regrowth is limited and debated, and the level is used as one input rather than a rule.

The practical point is that "normal" and "optimal for hair" are not the same conversation. A ferritin of 22 ug/L with heavy periods and daily shedding tells a fuller story than the word "normal" on a report, and it is the sort of result a doctor will want to act on and recheck. Whether anything is needed, and what, is a clinical decision, not something to sort out from a number alone.

One caveat: ferritin rises with infection and inflammation, so a test taken while you are unwell can read falsely reassuring. Wait a couple of weeks after an illness.

Thyroid, androgens, vitamin D and zinc

The rest of the first-line set covers the other common contributors.

• TSH and free T4. Both an under-active and an over-active thyroid cause diffuse hair loss. Under-active thyroid tends to bring dry, coarse hair with tiredness, feeling cold and heavier periods; over-active tends to bring fine shedding with anxiety, heat intolerance and lighter periods. Thyroid disorders are far more common in women, and the hair change is often what finally prompts the test.
• Total testosterone, SHBG, free androgen index and DHEA-S. Androgens shrink scalp follicles in women who are genetically sensitive to them. Most women with pattern thinning have androgen levels inside the normal range, so a normal result does not rule the pattern out. What testing does find is the minority whose androgens are genuinely raised, which changes what a doctor looks for next. Testosterone and DHEA-S well above range, particularly with rapid hair loss, deepening voice or facial hair changes, always needs a doctor's assessment.
• Vitamin D. Low vitamin D is very common in Australian women and is associated with several hair-loss patterns. The association is not the same as proof of cause, but it is cheap to measure and worth knowing.
• Zinc. Genuine zinc deficiency causes hair loss, though it is much less common in Australia than low iron. It is included because it is one of the few nutrient markers with a real evidence base for hair, unlike most of what gets marketed for hair and nails.

Two more worth knowing about. Prolactin and a coeliac screen are sometimes added when cycles have stopped or when there are gut symptoms alongside the shedding. And high-dose biotin, sold heavily for hair, interferes with several laboratory assays including thyroid; pause it for 72 hours before any collection or your results may be wrong.

Postpartum and perimenopausal hair loss

Two life stages produce shedding so predictably that they deserve naming.

Postpartum. Oestrogen keeps hair in its growing phase through pregnancy, so shedding pauses. After birth the hormone drop releases all of that hair at once, and the peak fall is usually around two to four months postpartum. It is normal and it settles over six to twelve months. What is worth testing is what sits underneath: blood loss at birth and breastfeeding both drain iron, and the thyroid can swing over-active then under-active in the first year. A postpartum blood check covers both.

Perimenopause. Falling oestrogen with relatively steadier androgens shifts the balance at the follicle, and thinning through the crown often starts or accelerates in the forties and fifties. Heavy perimenopausal bleeding drains iron at the same time, so the two causes frequently stack. Testing is about separating what is hormonal transition from what is correctable.

What to do with a normal result

A completely normal panel is common with pattern hair loss, and it is still worth having. It means the shedding is not being driven by low iron, thyroid dysfunction or an androgen excess, and it removes the guesswork so the next conversation is about the pattern itself.

That next conversation belongs with a GP or dermatologist, who can examine your scalp, confirm the type of hair loss and talk through the options that suit it. Hair recovery, when a cause is found and dealt with, is slow: hair grows roughly a centimetre a month, so give any change three to six months before judging it.

Borderline results are the ones worth pushing on. A ferritin in the low thirties, or a TSH at the top of the range, is technically normal and clinically interesting when you are shedding daily.

Your KnowLuna female hair loss check

The KnowLuna female hair loss check covers the four common causes in one blood collection, at an accredited Australian centre or with a home kit or a nurse visit: iron studies and full blood count, TSH and free T4, total testosterone with SHBG and free androgen index, DHEA-S, vitamin D and zinc.

Collect in the morning, avoid testing while unwell, and if you have cycles, day 2 to 5 gives the most interpretable androgen results. Your report explains each marker against your laboratory's range in plain English, and an AHPRA-registered doctor follows up anything abnormal.

Common questions

Sources and further reading

• Pathology Tests Explained (RCPA): ferritin
• Pathology Tests Explained (RCPA): thyroid function tests
• Pathology Tests Explained (RCPA): testosterone
• Healthdirect: female pattern hair loss
• Better Health Channel: patterned hair loss
• Jean Hailes: hair loss in women

General information only, not medical advice. If your symptoms are severe or sudden, see a doctor promptly. This page does not replace a consultation with a doctor who knows your history; read our medical disclaimer.