Overview.
Hair loss is among the most common dermatological complaints worldwide. Lab testing is most valuable when hair loss is diffuse, new onset, or accompanied by other symptoms. In women especially, coexisting hormonal and nutritional deficiencies (iron deficiency, thyroid dysfunction, androgen excess) should always be assessed — they are treatable contributors in the majority of cases.
Androgenetic alopecia: genetically determined follicular miniaturization driven by androgens; temporal/crown pattern in men; diffuse apical thinning with frontal hairline preservation in women (Ludwig pattern). Telogen effluvium: diffuse shedding 2-3 months after a physiological trigger. Chronic telogen effluvium: persistent shedding from ongoing causes (iron deficiency, thyroid disease).
Prevalence: AGA affects ~50% of men by age 50 and ~30-50% of women by age 70. In women with hair loss, iron deficiency accounts for up to 70% of identified metabolic causes; thyroid disease for 7.7%.
What to test.
First-line tests
- TSH — Thyroid dysfunction is one of the most common reversible causes; both hypo and hyperthyroidism cause telogen effluvium
- Ferritin — Most sensitive iron marker for hair loss; target >60-70 ng/mL; normal CBC does not exclude iron deficiency
- CBC (Complete Blood Count) — Screens for anaemia; insensitive for iron deficiency without anaemia
- Total Testosterone — Elevated in women with androgen-excess pattern hair loss; integral to PCOS workup
- SHBG — Low SHBG amplifies androgen bioavailability; low SHBG + normal total T = elevated free androgens
Second-line tests
- DHEA-S — Adrenal androgen marker; >700 mcg/dL warrants adrenal imaging
- Prolactin — Check if menstrual irregularity accompanies hair loss
- Vitamin D (25-OH) — Deficiency linked to hair follicle cycling disruption
- Vitamin B12 — Deficiency causes diffuse hair loss
- Serum Iron + TIBC — Confirms iron deficiency context when ferritin borderline
- 17-OH Progesterone — If non-classic CAH suspected (PCOS-like picture with hair loss)
- TPO Antibodies — If thyroid autoimmunity suspected even with normal TSH
Common causes.
- Iron Deficiency (Most common nutritional cause in women; up to 70% of metabolic hair loss cases)
- Hypothyroidism (Common; both hypo and hyperthyroid cause telogen effluvium)
- PCOS (androgen excess) (~25-40% of women with FPHL have PCOS or biochemical hyperandrogenism)
- Androgenetic Alopecia (genetic) (Most common overall; genetic predisposition driven by DHT sensitivity)
- Post-partum telogen effluvium (Common; estrogen withdrawal after delivery; typically self-resolving)
- Hyperprolactinemia (Less common; check if menstrual irregularity coexists)
- Vitamin D deficiency (Emerging association; measure if other causes excluded)
FAQs.
Should women with hair loss always get hormones tested?
Yes. In women with new-onset diffuse hair loss or a pattern consistent with FPHL, a hormonal and nutritional panel is recommended. Coexisting iron deficiency, thyroid dysfunction, and androgen excess are common, treatable, and can significantly contribute to or worsen hair loss.
Will treating iron deficiency reverse my hair loss?
If iron deficiency is the primary or contributing cause, correcting it (target ferritin >70 ng/mL) can halt active shedding and allow regrowth over 6-12 months. However, regrowth is not guaranteed — it depends on duration of deficiency and degree of follicular miniaturization. Treatment takes time.
Is DHT measured in a blood test for hair loss?
DHT can be measured by serum assay but is not routinely ordered for AGA in clinical practice. The pathological process is follicular sensitivity to DHT, not necessarily elevated circulating levels. Total testosterone, free androgen index, and SHBG provide more clinically actionable information.