What laboratory tests are recommended for patients presenting with hair loss?

Laboratory Testing for Hair Loss

For most patients with clinically evident alopecia areata, laboratory investigations are unnecessary as the diagnosis is made clinically, but when the diagnosis is uncertain or other systemic causes are suspected, targeted laboratory testing should include thyroid function (TSH), serum ferritin, vitamin D, zinc levels, and hormonal evaluation in women with signs of androgen excess. 1

When Laboratory Testing is NOT Needed

• Investigations are unnecessary in most cases of alopecia areata when the diagnosis is clinically evident 1
• Dermoscopy (trichoscopy) can confirm alopecia areata by identifying yellow dots, exclamation mark hairs, and cadaverized hairs without requiring blood work 1
• Ordering excessive laboratory tests when the diagnosis is clinically clear should be avoided 1

When Laboratory Testing IS Indicated

Laboratory tests should be considered in the following scenarios:

• When the diagnosis is uncertain or atypical presentation 1
• When other conditions in the differential diagnosis need to be ruled out 1
• When systemic causes of hair loss are suspected based on clinical history 2, 3

Recommended Laboratory Tests by Clinical Scenario

Core Nutritional Panel (for diffuse hair loss or suspected deficiencies):

• Serum ferritin - Iron deficiency is the most common nutritional deficiency worldwide and a sign of chronic diffuse telogen hair loss 4

  • Multiple studies show lower ferritin levels in women with alopecia areata and androgenetic alopecia 4
  • However, evidence remains mixed, with some large studies showing no association 4

• Vitamin D (25-hydroxyvitamin D) - Multiple case-control studies demonstrate lower serum vitamin D levels in alopecia areata patients compared to controls 4

  • Vitamin D deficiency (defined as <20 ng/mL or <50 nmol/L) shows inverse correlation with disease severity 4
  • Prevalence of vitamin D deficiency was 70% in alopecia areata patients versus 25% in controls in one study 4

• Serum zinc levels - Zinc deficiency is associated with hair loss, with serum zinc levels tending to be lower in patients with alopecia areata 1

  • Zinc serves as a cofactor for multiple enzymes and plays a role in hair follicle function 4

• Folate levels - Folate deficiency may contribute to hair loss 1

Thyroid Function Testing:

• Thyroid stimulating hormone (TSH) - Should be checked to rule out thyroid disease, which can cause hair loss 1
• Free T4 - Indicated when hypothyroidism is suspected based on symptoms (unexplained fatigue, weight gain, hair loss, cold intolerance, constipation, depression) 4
• High TSH with low free T4 indicates biochemical hypothyroidism 4
• Thyroid peroxidase (TPO) antibody testing is warranted if biochemical hypothyroidism is confirmed 4

Hormonal Evaluation (for women with signs of androgen excess):

Test for the following when women present with hair loss plus acne, hirsutism, or irregular periods: 1

• Total testosterone or bioavailable/free testosterone levels 1
• Sex hormone binding globulin (SHBG) levels 1
• Consider testing for polycystic ovary syndrome (PCOS) 1
• Prolactin level if hyperprolactinemia is suspected 1
• Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected 1
• Fasting lipid and lipoprotein levels to evaluate for dyslipidemia 1

Additional Testing Based on Differential Diagnosis:

• Fungal culture - When tinea capitis (scalp ringworm) is suspected 1, 5
• Serology for lupus erythematosus - When systemic lupus is in the differential diagnosis 1, 5
• Serology for syphilis - When secondary syphilis is suspected 1, 5
• Skin biopsy - Recommended for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose 1, 5

Common Pitfalls to Avoid

• Failing to consider the psychological impact of alopecia areata, which may warrant assessment for anxiety and depression 1
• Overlooking dermoscopy as a non-invasive diagnostic tool that can provide valuable diagnostic information before ordering laboratory tests 1
• Ordering comprehensive metabolic panels reflexively without clinical indication 1
• Missing endocrine disorders that may present with hair loss, including hypopituitarism, hypothyroidism, hyperthyroidism, diabetes mellitus, hyperprolactinemia, and Cushing syndrome 2

Differential Diagnosis Requiring Different Laboratory Approaches

Consider these conditions when evaluating hair loss: 1

• Trichotillomania (compulsive hair pulling) - clinical diagnosis, no labs needed
• Tinea capitis - requires fungal culture
• Early scarring alopecia - requires biopsy
• Telogen effluvium - may need nutritional panel
• Anagen effluvium (drug-induced) - clinical history
• Systemic lupus erythematosus - requires serology
• Secondary syphilis - requires serology