Laboratory Workup for Hair Loss
Order CBC, serum ferritin, and TSH as essential first-line tests for any patient presenting with hair loss, with ferritin being the single most important test for assessing iron stores. 1
Essential First-Line Laboratory Tests
All patients with hair loss should receive:
- Complete blood count (CBC) to assess for anemia 1
- Serum ferritin as the primary indicator of iron status and total iron storage, with ferritin ≤15 μg/L confirming iron deficiency with 98% specificity in premenopausal women 1
- Thyroid stimulating hormone (TSH) and free T4 to rule out thyroid disease, which is a common cause of hair loss 1
- Transferrin saturation to further evaluate iron status 1
Iron deficiency accounts for 70% of female alopecia cases, making ferritin the most critical test 2. The adequate ferritin level for hair growth is 40-60 ng/mL, corresponding to hemoglobin levels of 13.1-13.8 g/dL—substantially higher than the traditional anemia threshold 2.
Additional Testing Based on Clinical Context
Consider these tests when specific clinical features are present:
- 25-hydroxyvitamin D levels should be checked, particularly in alopecia areata, as 70% of alopecia areata patients have deficiency (<20 ng/mL) versus 25% of controls, with lower levels correlating inversely with disease severity 3
- Serum zinc if there is unexplained anemia, resistant alopecia areata (>6 months duration), or changes in taste acuity, though evidence for routine screening is conflicting 3, 1
- Thyroid peroxidase (TPO) antibody if biochemical hypothyroidism is confirmed or if unexplained fatigue and weight changes are present 3, 1
Hormonal Evaluation in Women with Signs of Androgen Excess
Order these tests if the patient has acne, hirsutism, or irregular periods:
- Total testosterone or bioavailable/free testosterone and sex hormone binding globulin (SHBG) levels 3
- Prolactin level if hyperprolactinemia is suspected 3
- Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected (PCOS evaluation) 3
- Fasting lipid and lipoprotein levels to evaluate for dyslipidemia associated with PCOS 3
- FSH and LH if gonadal dysfunction is suspected 1
Tests to Consider for Specific Differential Diagnoses
When the diagnosis is uncertain or presentation is atypical:
- Fungal culture when tinea capitis (scalp ringworm) is suspected 3
- Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 3
- Serology for syphilis when secondary syphilis is suspected 3
- Skin biopsy for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose 3
What NOT to Routinely Check
Avoid unnecessary testing:
- Vitamin B12: Insufficient evidence linking B12 deficiency to alopecia areata 1
- Serum copper, magnesium, and selenium: Current evidence is insufficient to recommend routine screening for alopecia areata 1
- Extensive autoimmune panels: Routine screening is probably not justified in most alopecia areata cases, though the condition is associated with other autoimmune diseases 1
Critical Clinical Pearls and Common Pitfalls
Avoid ordering excessive laboratory tests when the diagnosis is clinically evident, as alopecia areata is typically diagnosed clinically through characteristic patchy hair loss, exclamation mark hairs, and dermoscopy findings (yellow dots, cadaverized hairs) 3.
Redefine normal ferritin levels for hair loss patients: Consider ferritin ≥60 ng/mL (corresponding to hemoglobin ≥13.0 g/dL) as the target for early diagnosis and treatment, rather than waiting for frank anemia 2. Iron supplementation started within 6 months of hair loss onset results in better prognosis 1, 2.
Do not overlook the psychological impact: Assess for anxiety and depression, as hair loss can cause considerable psychological and social disability 3.
Remember that 34-50% of alopecia areata cases recover spontaneously within one year, making the tendency to spontaneous remission an important consideration before initiating aggressive workup 3.