Blood Tests for Hair Loss: What Clinicians Check

Blood Tests for Hair Loss at a Glance

Clinicians evaluate multiple biological markers when investigating potential contributors to hair shedding. According to Healthline, blood tests used when investigating hair loss include markers for blood counts, nutrient stores, thyroid function, and hormone activity.

Iron and Ferritin

A complete blood count (CBC) measures red and white blood cells, hemoglobin, and platelets. Healthline states that a CBC helps diagnose anemia, which can cause hair loss when iron is insufficient.

Iron produces hemoglobin that carries oxygen to follicles. Low ferritin suggests depleted iron reserves, which can weaken hair and cause shedding (see information on iron levels).

Low ferritin suggests depleted iron reserves. Reference ranges for ferritin vary by laboratory, and a clinician interprets individual values.

Thyroid Tests

Thyroid-stimulating hormone evaluates thyroid gland function. Healthline notes that both an underactive thyroid and an overactive thyroid can cause hair thinning (see details on a thyroid panel and symptoms of hypothyroidism).

A clinician interprets TSH results against the lab's own ranges.

Vitamin D and B12

Healthline lists vitamin D and B12 among tests used when investigating hair loss.

A clinician determines whether evaluating vitamin D levels or vitamin B12 levels is appropriate for a patient's evaluation.

Hormone and Autoimmune Tests

Sex hormone tests can help identify male pattern baldness and hair loss related to polycystic ovary syndrome (PCOS). Healthline lists testosterone, estrogen, and dihydrotestosterone (DHT) among the hormones evaluated during an assessment (see information on hormone testing and PCOS).

Antinuclear antibody (ANA) testing can identify autoimmune disorders such as lupus and scarring hair loss from autoimmune conditions. Healthline also lists inflammatory markers, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), blood glucose, syphilis testing, and cortisol levels among tests used in hair loss investigations.

A clinician interprets these results.

Why Normal Results Still Leave Questions

According to Cleveland Clinic, telogen effluvium is diagnosed by a physical exam with a pull test and a review of diet and medical history (see the guide to telogen effluvium).

Cleveland Clinic also states that diagnosing female pattern hair loss involves a scalp exam, hair samples, scalp biopsy, and blood tests if other conditions are suspected (see Cleveland Clinic on female pattern baldness).

Biotin Before a Blood Draw

Biotin supplements can alter certain laboratory findings. An ASA reproduction of the FDA biotin safety communication states that biotin can cause clinically significant incorrect lab test results.

Individuals who take biotin supplements should notify their clinician before undergoing blood testing (see the guide to biotin for hair loss).

When to See a Doctor

Healthline recommends seeking clinical care for excessive shedding, sudden or patchy hair loss, scalp thinning, or hair loss that begins after starting a medication.

Evaluation is also advised if hair loss occurs alongside scalp redness, itching, or pain, or symptoms such as fatigue, weight changes, or menstrual irregularities.

This page is educational and not a substitute for a clinician's advice.