What lab workup is recommended for a patient presenting with hair loss?

Laboratory Workup for Hair Loss

Order CBC, serum ferritin, and TSH as essential first-line tests for any patient presenting with hair loss, as these identify the most common treatable causes including iron deficiency, anemia, and thyroid disease. 1

Essential First-Line Laboratory Tests

Iron Studies (Most Important)

• Serum ferritin is the single most important test for evaluating iron stores in hair loss patients 1
• Ferritin ≤15 μg/L confirms iron deficiency with 98% specificity in premenopausal women 1
• Iron deficiency accounts for 70% of female alopecia cases, making it the most common nutritional cause 2
• Complete blood count (CBC) should be ordered to assess for anemia 1
• Transferrin saturation should be checked as part of the iron workup 1
• The adequate ferritin level for hair growth is 40-60 ng/mL (corresponding hemoglobin ≥13.0 g/dL), which is higher than the threshold for anemia 2

Thyroid Function

• TSH and free T4 should be checked in all patients with hair loss 1
• Thyroid peroxidase (TPO) antibody testing should be considered if biochemical hypothyroidism is confirmed or if patients have unexplained fatigue, weight changes, or other thyroid symptoms 3, 1
• Thyroid disease is associated with alopecia areata and can independently cause hair loss 3

Additional Testing Based on Clinical Context

Vitamin D

• 25-hydroxyvitamin D levels should be checked, particularly in alopecia areata patients 3, 1
• 70% of alopecia areata patients have vitamin D deficiency (<20 ng/mL) versus 25% of controls, with lower levels correlating inversely with disease severity 3
• Target serum 25-hydroxyvitamin D levels ≥75 nmol/L 1

Zinc

• Serum/plasma zinc should be checked if there is unexplained anemia, hair loss, or changes in taste acuity 1
• Serum zinc levels tend to be lower in alopecia areata patients, particularly those with resistant disease >6 months duration 3
• Evidence for zinc deficiency in alopecia areata is conflicting, with insufficient data to recommend routine screening 1

Hormonal Testing (For Women with Signs of Androgen Excess)

• Total testosterone or bioavailable/free testosterone levels and sex hormone binding globulin (SHBG) should be tested in women with signs of androgen excess such as acne, hirsutism, and irregular periods 3
• Consider testing for polycystic ovary syndrome (PCOS) in women with these signs 3
• Check prolactin level if hyperprolactinemia is suspected 3
• Perform two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected 3
• Assess fasting lipid and lipoprotein levels to evaluate for dyslipidemia 3
• FSH and LH should be checked if gonadal dysfunction is suspected 1

Specialized Testing When Indicated

• Fungal culture is recommended when tinea capitis (scalp ringworm) is suspected 3
• Skin biopsy is recommended for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose 3
• Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 3
• Serology for syphilis when secondary syphilis is suspected 3

What NOT to Routinely Check

• Vitamin B12: Insufficient evidence linking B12 deficiency to alopecia areata 1
• Routine screening for copper, magnesium, and selenium: Current evidence is insufficient to recommend routine screening for alopecia areata 1
• Iron studies specifically for 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 compared to other hair loss types 1

Critical Clinical Considerations

When Laboratory Testing May Be Unnecessary

• Investigations are unnecessary in most cases of alopecia areata when the diagnosis is clinically evident (patchy, non-scarring hair loss with exclamation mark hairs) 3
• Laboratory tests should be considered when the diagnosis is uncertain, presentation is atypical, or when other conditions in the differential diagnosis need to be ruled out 3

Timing and Prognosis

• Iron supplementation started within 6 months of hair loss onset results in better prognosis 1, 2
• Disease duration is an important prognostic factor for improvement with iron supplementation 2
• The onset of hair loss due to iron deficiency develops gradually over months 4

Common Pitfalls to Avoid

• Avoid ordering excessive laboratory tests when the diagnosis is clinically evident, as alopecia areata is typically diagnosed clinically 3
• Do not overlook dermoscopy as a non-invasive diagnostic tool that can identify yellow dots, exclamation mark hairs, and cadaverized hairs in alopecia areata 3
• Failing to consider the psychological impact of hair loss, which may warrant assessment for anxiety and depression 3
• The decision to treat iron deficiency without anemia remains controversial, though treating iron deficiency anemia is clearly indicated 1, 5