What labs should be checked in a patient with hair loss and normal thyroid function?

Laboratory Workup for Hair Loss with Normal Thyroid Function

Essential Laboratory Tests to Order

Check iron stores (ferritin), vitamin D, and zinc levels as the primary laboratory evaluation for hair loss when thyroid function is normal. 1

Core Laboratory Panel

• Ferritin (iron stores) - Essential marker for iron deficiency, which commonly causes telogen effluvium and diffuse hair loss even before anemia develops 1

• Vitamin D (25-hydroxyvitamin D) - Deficiency associated with hair follicle cycling abnormalities and hair loss 1

• Zinc levels - Zinc deficiency can cause telogen effluvium and impaired hair growth 1

Confirm Thyroid Status is Truly Normal

• Verify both TSH and free T4 were measured - TSH alone may miss subclinical thyroid dysfunction; normal TSH with normal free T4 definitively excludes thyroid-related hair loss 2

• Consider anti-TPO antibodies - Positive antibodies indicate autoimmune thyroid disease (Hashimoto's) which can cause hair loss even with normal hormone levels, particularly in alopecia areata 2, 3

Additional Testing Based on Clinical Pattern

For Women with Androgenic Pattern Hair Loss

• Total testosterone, free testosterone, DHEA-S - Evaluate for hyperandrogenism if hair loss shows frontal/vertex thinning pattern 4

• Prolactin - Elevated levels associated with hair loss in hyperprolactinemic states 4

• Fasting glucose or HbA1c - Diabetes mellitus associates with hair disorders 5, 6

For Autoimmune-Pattern Hair Loss (Alopecia Areata)

• Fasting blood glucose - Screen for incipient diabetes mellitus, which commonly coexists with alopecia areata 6

• Complete blood count - Evaluate for associated autoimmune conditions 3

• Anti-TPO antibodies - Even with normal TSH/T4, positive antibodies suggest autoimmune predisposition and may indicate more severe alopecia areata 3

Critical Diagnostic Considerations

Why Normal Thyroid Function Doesn't Exclude Thyroid-Related Hair Loss

• Subclinical thyroid dysfunction may manifest as hair loss before hormone levels become overtly abnormal 3

• Positive anti-thyroid antibodies with normal hormone values can still cause or worsen alopecia areata 3

• Autoimmune thyroid disease shares common pathways with alopecia areata through autoimmune polyglandular syndromes 3

Common Pitfalls to Avoid

• Don't assume "normal thyroid" means thyroid is irrelevant - Verify that both TSH and free T4 were checked, not just TSH alone 2

• Don't skip anti-TPO antibodies in alopecia areata - Positive antibodies predict more severe disease even with normal hormone levels 3

• Don't overlook nutritional deficiencies - Ferritin, vitamin D, and zinc are frequently deficient in hair loss patients and are easily correctable 1

Algorithmic Approach to Laboratory Testing

1. First-line labs for all patients with hair loss and normal thyroid:

   • Ferritin
   • Vitamin D (25-OH vitamin D)
   • Zinc level 1

2. If diffuse hair loss (telogen effluvium pattern):

   • Add complete blood count
   • Consider inflammatory markers if systemic illness suspected 5

3. If androgenic pattern (frontal/vertex thinning in women):

   • Total and free testosterone
   • DHEA-S
   • Prolactin
   • Fasting glucose 4

4. If patchy hair loss (alopecia areata):

   • Anti-TPO antibodies (even with normal TSH/T4)
   • Fasting glucose or HbA1c
   • Consider complete autoimmune panel if family history positive 6, 3

5. If postmenopausal woman with frontal fibrosing alopecia:

   • Comprehensive thyroid panel including antibodies (up to 50% have thyroid conditions)
   • Hormone panel 3