Blood tests for hair thinning: what they check

Hair thinning can follow illness, stress, hormonal change, nutritional deficiency, medication use or an inherited pattern. A clinician may examine the scalp, ask when shedding began and look for broken hairs, scaling or smooth patches before choosing blood tests. Testing may include a blood count, iron assessment, thyroid checks or other tests guided by symptoms. A normal result does not explain every type of hair loss, and an abnormal result does not prove it is the only cause. Hair changes often become noticeable after the event that triggered them.

Make a list of medicines, supplements, recent illness, major stress, dietary changes and family hair patterns. Mention heavy menstrual bleeding, restrictive eating, bowel symptoms, cold intolerance or changes in weight because these details can guide testing. Do not start high-dose supplements before discussing them; they may alter results or cause harm. Take photographs in similar lighting if the thinning is changing, and follow the clinician's plan rather than treating a laboratory result in isolation.

Arrange a prompt review if hair loss is sudden, occurs in sharply defined patches, involves eyebrow or body hair, or comes with scalp pain, redness, pus or heavy scaling. Seek urgent help for hair loss with severe weakness, fainting, breathlessness or other signs of significant illness. Earlier assessment can help identify inflammation, infection or a treatable underlying problem.

Ask which causes your hair pattern suggests, which blood tests are appropriate, whether supplements or medicines could affect the results, and when improvement might be expected after treating an identified cause. Ask whether a dermatologist should examine the scalp.