Laboratory Workup for Hair Loss with Normal Thyroid Function

Essential Laboratory Tests to Order

The American College of Oncology recommends checking iron stores (ferritin), vitamin D, and zinc levels as the primary laboratory evaluation for hair loss when thyroid function is normal 1
Ferritin is an essential marker for iron deficiency, which commonly causes telogen effluvium and diffuse hair loss even before anemia develops 1
Vitamin D deficiency is associated with hair follicle cycling abnormalities and hair loss 1
Zinc deficiency can cause telogen effluvium and impaired hair growth 1

The American Thyroid Association recommends verifying both TSH and free T4 were measured to exclude thyroid-related hair loss, as TSH alone may miss subclinical thyroid dysfunction 2
The American Thyroid Association suggests considering anti-TPO antibodies, as positive antibodies indicate autoimmune thyroid disease (Hashimoto's) which can cause hair loss even with normal hormone levels 2

The American College of Oncology emphasizes the importance of not overlooking nutritional deficiencies, such as ferritin, vitamin D, and zinc, which are frequently deficient in hair loss patients and are easily correctable 1
The American Thyroid Association advises against assuming "normal thyroid" means thyroid is irrelevant, and recommends verifying that both TSH and free T4 were checked, not just TSH alone 2