When is hair fall medically significant?
Losing 50–100 hairs per day is normal. Medically significant hair loss (alopecia) means visible thinning, widening parting, receding hairline, or clumps of hair coming out during washing or brushing. Before treating hair loss, finding the cause is essential — the wrong treatment won't work.
Blood tests for hair fall
1. TSH (Thyroid) — Most important first test
Both hypothyroidism (high TSH) and hyperthyroidism (low TSH) cause hair loss. Thyroid-related hair loss affects the entire scalp uniformly (diffuse thinning), including outer third of eyebrows in hypothyroidism. Hair regrows once thyroid is treated. Always test TSH first for hair loss — it's the most correctable cause.
2. Ferritin — Low iron stores cause hair shedding
Low ferritin is the most common nutritional cause of hair loss in women, especially those with heavy periods. Hair follicles need iron to function. Ferritin below 30 ng/mL can cause significant hair shedding — even when haemoglobin is still normal. This is why ferritin must be tested specifically for hair loss; a normal CBC does not rule it out.
3. Vitamin D
Vitamin D receptors are present in hair follicles. Deficiency (below 20 ng/mL) is associated with alopecia areata (patchy hair loss) and diffuse thinning. Very common in India due to indoor lifestyles. Correcting Vitamin D doesn't always immediately reverse hair loss but is an important part of treatment.
4. Vitamin B12
B12 is essential for rapidly dividing cells — including hair follicle cells. Deficiency causes premature hair loss. Especially common in strict vegetarians. B12 below 200 pg/mL needs treatment.
5. Testosterone / DHEA-S / LH:FSH (for women)
Hormonal hair loss (androgenic alopecia) in women is caused by excess androgens. Testing testosterone and DHEA-S, along with LH:FSH ratio, helps identify PCOS or adrenal causes. Pattern: diffuse thinning at the crown, no frontal hairline recession (unlike male pattern baldness).
6. Zinc and Biotin (less commonly tested)
Zinc deficiency can cause hair loss, especially in people on restrictive diets. Biotin deficiency is often marketed but is actually very rare as a cause of hair loss in otherwise healthy people. Most "biotin supplements for hair" lack strong evidence — treat proven deficiencies first.
Questions to ask your doctor
- My ferritin is 25 ng/mL — is that low enough to cause hair loss?
- I have normal TSH but still losing hair — what else should we check?
- Do I need to see a dermatologist for a scalp examination?
- How long after treating the deficiency will my hair start regrowing?