Laboratory Testing for Hair Loss in Teenagers
For teenage patients with hair loss, investigations are generally unnecessary in most cases, particularly for alopecia areata, but when indicated, obtain: CBC, ferritin, TSH, vitamin D 25-OH, and consider zinc levels 1, 2, 3.
Clinical Context Determines Testing Strategy
The approach to laboratory testing depends heavily on the clinical presentation and pattern of hair loss:
For Patchy Hair Loss (Alopecia Areata Pattern)
- Routine laboratory screening is NOT recommended 1
- The diagnosis is primarily clinical based on examination findings (exclamation mark hairs, yellow dots on dermoscopy)
- Testing should only be pursued when the diagnosis is uncertain or to rule out specific differential diagnoses:
- Fungal culture if tinea capitis suspected
- Serology for lupus or syphilis if clinically indicated
- Scalp biopsy when diagnosis remains unclear
Important caveat: Despite increased frequency of autoimmune diseases in alopecia areata patients, routine autoimmune screening is not justified 1. The evidence for iron deficiency in alopecia areata is contradictory, and routine iron testing is not recommended since supplementation has not shown treatment benefit 1.
For Diffuse or Pattern Hair Loss (Female Pattern Hair Loss)
Mandatory testing 2:
- Androgen assessment: Total testosterone (preferably by LC/MS) and free testosterone (by equilibrium dialysis or calculated using SHBG)
- SHBG for calculating free testosterone
Optional but recommended 2:
- Iron studies (ferritin) - though evidence is mixed on its relationship to hair loss
- Vitamin D (25-hydroxyvitamin D) - 62% of FPHL patients show deficiency
- Zinc levels - 15% of FPHL patients show deficiency
- Thyroid profile (TSH, free T4)
- Prolactin
Universal Baseline Panel for Unclear Cases
When the diagnosis is not immediately apparent, a reasonable screening panel includes 3:
- Complete blood count
- Ferritin
- TSH
- Vitamin D 25-OH
Key Clinical Pitfalls
Do not over-test: The most common mistake is ordering extensive hormonal panels in alopecia areata where they provide no diagnostic or therapeutic value 1. One study showed that despite 40% of female patients reporting symptoms suggestive of hormonal disorders, hormone testing revealed no significant abnormalities 4.
Recognize age-specific patterns: In children and adolescents, the most common causes differ from adults - tinea capitis (47.4%), alopecia areata (37.9%), and telogen effluvium (8.8%) dominate 5. Simple bedside tests (KOH mount, hair shaft microscopy, hair pull test) often provide more diagnostic value than laboratory testing 5, 6.
Pattern recognition guides testing: Distinguish between patchy versus diffuse hair loss, and scarring versus non-scarring patterns. This clinical assessment determines whether laboratory testing is even necessary 3, 7.
Evidence Quality Note
The 2019 Androgen Excess and PCOS Committee guidelines 2 provide the most comprehensive and recent evidence-based recommendations for pattern hair loss, while the 2012 British Association of Dermatologists guidelines 1 remain authoritative for alopecia areata despite being older, as their core recommendations align with more recent consensus documents 8, 9, 10.