Pattern hair loss does not show up on a blood test. But several conditions that cause or worsen hair loss do, and they are treatable — which makes testing the step with the best return on money spent.
This matters more if your hair loss is diffuse rather than patterned, came on relatively quickly, or is happening alongside other symptoms such as fatigue, weight change or heavy periods.
The Tests Worth Having
Ferritin
The measure of iron stores, and the single most useful test in this context. Low ferritin is associated with hair shedding even when full-blown anaemia is absent — so a normal full blood count does not rule it out. Ask specifically for ferritin, not just "iron levels".
Thyroid function
Both underactive and overactive thyroid cause hair loss, and both are common and eminently treatable.
Full blood count
Picks up anaemia and other general abnormalities.
Vitamin D
Deficiency is common in the UK, particularly over winter, and has been associated with hair loss.
For women, where indicated
Testosterone and other androgens, particularly where there are signs of PCOS such as irregular periods, acne or unwanted facial hair.
Tests That Are Usually Marketing
Private hair-loss panels often include a long list of extras. Be sceptical of:
- Broad "hair mineral analysis" from hair samples — not a validated diagnostic method
- Extensive vitamin panels in people eating a normal diet with no symptoms of deficiency
- Food intolerance testing, which has no established role in hair loss
- Genetic "baldness risk" tests, which mostly tell you what a family photograph already told you
A long panel looks thorough and mostly generates normal results and a bill.
Where to Get Tested
Start with your GP. If you have diffuse hair loss with any suggestion of a systemic cause, this is a legitimate reason to be seen, and NHS testing costs you nothing.
Private testing is an option if you want it faster or your GP declines. If you go private, choose a focused panel over a maximal one, and take the results back to a doctor to interpret — a number outside a reference range is not a diagnosis.
What Happens If Something Is Low
Treating the deficiency comes first. Hair recovery from correcting low ferritin or thyroid dysfunction takes months, because hair grows slowly and the follicles have to re-enter their growth phase — expect three to six months before judging.
Do not start iron supplementation on the basis of an internet result. Iron overload is harmful, and unexplained iron deficiency itself needs investigating rather than simply topping up.
The Weight-Loss Connection
Shedding a few months after significant rapid weight loss — including on GLP-1 medication — is a recognised telogen effluvium pattern and is usually temporary. It is worth checking ferritin in that situation, since reduced food intake can genuinely lower iron stores, but the shedding itself often resolves without treatment.
The Order That Makes Sense
- Rule out reversible causes with a focused blood test
- Treat anything found, and give it months
- Then, if pattern hair loss remains the explanation, consider treatment for that
Doing it in the other order means paying indefinitely for a treatment aimed at the wrong problem.