Blood Tests for Hair Loss: Lab Tests That Reveal Why Your Hair Is Thinning

Noticing more hair in your brush, on your pillow, or clogging your drain? Hair loss in women is distressing - and often dismissed as "just stress" or "normal aging." But here's the truth: hair loss is frequently a symptom of an underlying, treatable condition.

According to research published in JAMA, the common causes of hair loss can often be identified through proper evaluation - and many are reversible once the root cause is addressed.

Your hair is a reflection of your internal health. When something is off - whether it's iron levels, thyroid function, or hormones - your hair is often one of the first places it shows.

Understanding Hair Loss Types

Before diving into tests, it helps to understand the main types of hair loss in women:

Telogen Effluvium

The most common type. Hair follicles prematurely enter the "resting" phase, causing diffuse shedding across the scalp. This typically occurs 2-3 months after a trigger event (stress, illness, nutrient deficiency, hormonal change).

Female Pattern Hair Loss (Androgenetic Alopecia)

Genetic and hormonal. Hair thins gradually at the crown and part line while the frontal hairline is preserved. Often related to androgen sensitivity.

Alopecia Areata

Autoimmune condition causing patchy, round bald spots. Associated with thyroid autoimmunity and other autoimmune conditions.

The Hair Loss Lab Panel: Essential Tests

1. Ferritin (Iron Storage)

This is the most important test for hair loss investigation.

A landmark study published in the Journal of the American Academy of Dermatology found that women with ferritin levels at or below 30 ng/mL had an odds ratio of 21.0 for telogen hair loss compared to those with higher levels. That's a 21-fold increased risk.

Additional research in Skin Pharmacology and Physiology confirmed that serum ferritin levels in women with telogen effluvium (14.7 ng/mL average) were significantly lower than in controls (43.5 ng/mL).

Optimal ferritin for hair: While labs list 12 ng/mL as the lower limit, most dermatologists recommend ferritin above 70 ng/mL for optimal hair growth.

2. Complete Thyroid Panel

Thyroid dysfunction is a major cause of hair loss in women. Research from JAMA Dermatology demonstrated that in hypothyroidism, more hair follicles shift into the telogen (resting) phase, causing diffuse thinning.

Tests to request:

• TSH - Often the only test ordered, but insufficient alone
• Free T4 - Storage form of thyroid hormone
• Free T3 - Active thyroid hormone
• TPO Antibodies - Hashimoto's thyroiditis marker
• Thyroglobulin Antibodies - Another autoimmune thyroid marker

A case report in JAMA described a woman with hair thinning and subclinical hypothyroidism - her hair improved with thyroid treatment.

3. Vitamin D

The same study in Skin Pharmacology and Physiology found that low vitamin D was associated with both telogen effluvium and female pattern hair loss. Vitamin D receptors are present in hair follicles and play a role in hair cycling.

Test: 25-hydroxyvitamin D. Optimal: 40-60 ng/mL

4. Complete Iron Panel

Beyond ferritin, a complete iron panel helps identify the type and severity of iron deficiency:

• Serum Iron - Circulating iron
• TIBC - Total iron binding capacity
• Transferrin Saturation - How much iron is bound

Research in the Journal of the American Academy of Dermatology reviewed the relationship between iron deficiency and hair loss, noting that iron is essential for the rapidly dividing cells in hair follicles.

5. Hormone Panel

Hormonal imbalances can trigger both telogen effluvium and pattern hair loss. Research in JAMA Dermatology evaluated hormone markers in female androgenic alopecia.

Tests to request:

• Testosterone (total and free) - Elevated levels can cause hair thinning
• DHEA-S - Adrenal androgen
• Estradiol - Primary estrogen
• Progesterone - Often low relative to estrogen
• SHBG - Sex hormone binding globulin (low levels = more free androgens)

6. Vitamin B12

B12 deficiency affects cell division throughout the body, including the rapidly dividing cells of hair follicles. Deficiency can contribute to hair thinning, especially in vegetarians/vegans.

Test: Vitamin B12. Optimal: 500-800 pg/mL

7. Zinc

Zinc is essential for hair tissue growth and repair. Deficiency has been associated with hair loss and can impair the function of hair follicles.

8. Complete Blood Count (CBC)

A comprehensive study of 2,851 women with telogen effluvium published in Dermatology Practical & Conceptual found that "deficiency of laboratory parameters, especially ferritin and serum iron, is a common finding in female patients presenting with TE."

What the Research Shows

A 2003 study published in the Journal of Investigative Dermatology found that mean ferritin levels in patients with androgenetic alopecia and alopecia areata were statistically significantly lower than in women without hair loss.

More recently, a 2024 study in the Journal of Cosmetic Dermatology conducted a comprehensive investigation of biochemical status in telogen effluvium patients, analyzing hemoglobin, ferritin, vitamin B12, vitamin D, thyroid function, zinc, copper, biotin, and selenium - confirming that multiple nutritional factors can contribute to hair loss.

When Hair Loss Needs Urgent Evaluation

While most hair loss is gradual and treatable, see a dermatologist promptly if you experience:

• Sudden, rapid hair loss
• Patchy bald spots (may indicate alopecia areata)
• Hair loss with scalp pain, burning, or itching
• Scarring or changes in scalp texture
• Hair loss accompanied by other symptoms (fatigue, weight changes, menstrual irregularity)

The Bottom Line

Hair loss is often your body's way of telling you something is off internally. The good news? Once you identify the cause through proper lab testing, many types of hair loss are reversible.

Don't accept vague reassurances that your hair loss is "just stress" or "normal." Request comprehensive testing - especially ferritin, thyroid, and vitamin D - and look at optimal ranges, not just "normal."

Your hair deserves answers. So do you.