What tests are performed to diagnose alopecia areata?

Diagnostic Tests for Alopecia Areata

The diagnosis of alopecia areata primarily relies on clinical examination including trichoscopy and hair pull test, with laboratory testing recommended only to rule out associated conditions or alternative diagnoses. 1

Clinical Examination

• Visual inspection: Look for characteristic nonscarring, well-demarcated patches of hair loss with preserved follicular ostia and normal underlying skin 1, 2
• Hair pull test: Positive test (easily extracted hairs) indicates active disease 2
• Trichoscopy/Dermoscopy: Non-invasive examination that reveals:
  • Yellow dots (most specific finding)
  • Exclamation mark hairs (tapering near the scalp)
  • Black dots (broken hairs)
  • Vellus hairs
  • Regrowth of white/depigmented hairs 1, 2

Laboratory Testing

When clinical presentation is atypical or to rule out associated conditions:

• Complete blood count: To exclude systemic causes of hair loss 1
• Ferritin levels: Iron deficiency is associated with chronic hair loss 1
• Thyroid stimulating hormone: Autoimmune thyroid disease is commonly associated with alopecia areata 1, 2
• Vitamin D 25OH levels: Lower levels are often found in alopecia areata patients 1
• Autoimmune markers: Consider in cases with suspected concurrent autoimmune conditions 1

Scalp Biopsy

• Not routinely required but may be helpful in:
  • Atypical presentations
  • Cases where clinical diagnosis is uncertain
  • Differentiating from other forms of alopecia 1, 3

Disease Severity Assessment Tools

• Severity of Alopecia Tool (SALT) score: Quantifies extent of scalp involvement; SALT score ≥20 indicates moderate-to-severe disease that may warrant systemic therapy 4
• Alopecia Areata Scale (AAS): Alternative classification system for disease severity 4

Differential Diagnosis Considerations

Tests may be needed to rule out other conditions that can mimic alopecia areata:

• KOH preparation/fungal culture: To exclude tinea capitis 2
• Syphilis serology: When syphilitic alopecia is suspected 2
• Clinical assessment for trichotillomania: Look for broken hairs of varying lengths and absence of exclamation mark hairs 2
• Biopsy: To differentiate from scarring alopecias when clinical features are unclear 2, 3

Common Pitfalls to Avoid

• Overreliance on laboratory testing: The diagnosis is primarily clinical; extensive laboratory workup is not necessary in typical cases 1, 3
• Missing associated conditions: Failing to screen for commonly associated autoimmune conditions (thyroid disease, vitiligo, atopy) 2
• Inadequate assessment of disease activity: Not performing hair pull test or trichoscopy to determine if the disease is active or in remission 1, 2
• Overlooking psychological impact: Alopecia areata significantly impacts quality of life and may require psychological support alongside medical treatment 4, 5

The diagnostic approach should be guided by clinical presentation, with laboratory testing tailored to rule out associated conditions or alternative diagnoses when the clinical picture is not straightforward.