What laboratory tests should be ordered to evaluate hair loss?

Laboratory Testing for Hair Loss Evaluation

Order CBC, serum ferritin, and TSH as baseline tests for any patient presenting with hair loss, with ferritin being the single most important test for iron stores. 1

Essential First-Line Laboratory Tests

Iron Studies (Most Critical)

• Serum ferritin is the primary indicator of iron status and total iron storage 2
• Ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 1
• However, ferritin ≥60 ng/mL (corresponding Hb ≥13.0 g/dL) should be considered the adequate level for hair growth, not just the absence of anemia 3
• Complete blood count (CBC) to assess for anemia 1
• Transferrin saturation 1
• Consider that the ferritin level corresponding to female anemia (Hb 12.0 g/dL) is only 5.1 ng/mL, which is far below the adequate level needed for hair growth (40-60 ng/mL) 3

Important caveat: Serum ferritin may be falsely elevated in patients with infectious, inflammatory, and neoplastic conditions, potentially masking iron deficiency 4. In these cases, additional tests like erythrocyte zinc protoporphyrin, transferrin concentration, serum iron, and transferrin saturation may be needed 4.

Thyroid Function

• TSH and free T4 should be checked in all patients with hair loss 1
• Thyroid dysfunction (hypothyroidism and hyperthyroidism) accounts for approximately 7.7% of female alopecia cases 3
• Unexplained fatigue, weight changes, or other thyroid symptoms warrant thyroid antibody testing (thyroid peroxidase antibody) 2

Additional Testing Based on Clinical Context

When to Check Additional Micronutrients

Zinc:

• Check serum/plasma zinc if there is unexplained anemia, hair loss, or changes in taste acuity 2
• Evidence for zinc deficiency in alopecia areata is conflicting, with insufficient data to recommend routine screening 2

Vitamin D:

• Multiple studies show lower vitamin D levels in alopecia areata patients (83.3% deficiency rate in one study) 2
• Consider checking 25-hydroxyvitamin D levels, particularly in alopecia areata 2
• Target serum 25-hydroxyvitamin D levels ≥75 nmol/L 2

Copper, Magnesium, Selenium:

• Check serum copper if there is unexplained anemia or poor wound healing 2
• Check selenium if there is chronic diarrhea, metabolic bone disease, unexplained anemia, or unexplained cardiomyopathy 2
• Current evidence is insufficient to recommend routine screening of these minerals for alopecia areata 2

Autoimmune and Hormonal Screening

Autoimmune markers:

• Consider autoimmune profile testing, as autoimmune diseases account for 14.8% of female alopecia cases 3
• Alopecia areata is associated with other autoimmune conditions, though routine screening is probably not justified in most cases 2

Hormonal evaluation:

• In women with signs of hyperandrogenism or irregular menses, consider testosterone, DHEA-S, and evaluation for polycystic ovary syndrome 5
• FSH and LH if gonadal dysfunction is suspected 2

What NOT to Routinely Check

• Vitamin B12: Insufficient evidence linking B12 deficiency to alopecia areata 2
• Iron studies in alopecia areata: The British Association of Dermatologists states routine testing for iron status is not recommended specifically for alopecia areata, as studies have not confirmed increased iron deficiency in this condition 2, 1
• However, iron deficiency is associated with telogen effluvium, androgenetic alopecia, and diffuse hair loss 2, 3

Critical Clinical Pearls

Timing matters for iron deficiency: Iron supplementation started within 6 months of hair loss onset results in better prognosis 1, 3. Disease duration is an important prognostic factor 3.

Iron deficiency without anemia: The decision to treat iron deficiency without anemia remains controversial 1, 4. However, recent evidence suggests ferritin levels adequate to prevent anemia (≥15 μg/L) are insufficient for optimal hair growth, which requires ferritin ≥60 ng/mL 3.

Gender considerations: Most iron deficiency studies in hair loss have been conducted exclusively in women 2. In premenopausal women, menstrual blood loss and pregnancy are the most common causes; in men and postmenopausal women, gastrointestinal blood loss and malabsorption should be investigated 4.

Diverse etiologies: Hair loss has multiple causes including nutritional deficiencies (83.9% of cases in one study), autoimmune diseases (14.8%), thyroid disorders (7.7%), psychological stress (12.3%), and even recent COVID-19 vaccination (6.5%) 3. This underscores the importance of comprehensive laboratory evaluation rather than assuming a single etiology.