Diagnostic Tests for Alopecia Areata
The diagnosis of alopecia areata primarily relies on clinical examination, with trichoscopy and dermoscopy being the most valuable non-invasive diagnostic tools, while laboratory tests are used to rule out associated conditions rather than confirm the diagnosis. 1
Clinical Examination
- Visual assessment: Look for characteristic non-scarring, well-circumscribed patches of hair loss with preserved follicular ostia
- Hair pull test: Positive test at the periphery of patches indicates active disease
- Exclamation mark hairs: Short broken hairs that taper proximally are pathognomonic signs 2
- Distribution pattern: Document the pattern (patchy, ophiasis, totalis, universalis) as this affects treatment approach
Specialized Diagnostic Tools
- Trichoscopy/Dermoscopy: First-line diagnostic tool with high accuracy 1
- Look for yellow dots (most specific finding)
- Black dots (cadaverized hairs)
- Broken hairs
- Tapered hairs (exclamation mark hairs)
- Regrowth of unpigmented/white hairs
Laboratory Testing
Laboratory tests are not diagnostic for alopecia areata but help rule out associated conditions:
- Complete blood count: To assess for underlying anemia or infection
- Ferritin levels: Iron deficiency is associated with hair loss conditions 1
- Thyroid stimulating hormone: Autoimmune thyroid disease is commonly associated with alopecia areata 2
- Vitamin D 25OH levels: Lower levels are associated with alopecia areata 1
- Autoimmune markers: Consider in cases with suspected autoimmune comorbidities
Scalp Biopsy
- Not routinely required but may be necessary in atypical cases or when diagnosis is uncertain
- Histopathology shows peribulbar lymphocytic infiltrate ("swarm of bees") around affected hair follicles
- Helps differentiate from other causes of hair loss when clinical diagnosis is challenging 3
Disease Severity Assessment
For treatment planning and monitoring, these standardized tools are used:
- Severity of Alopecia Tool (SALT) score: Quantifies percentage of scalp involvement 4
- Alopecia Areata Scale (AAS): Categorizes severity 4
Differential Diagnosis Considerations
- Trichotillomania: Look for broken hairs of varying lengths and absence of exclamation mark hairs
- Tinea capitis: Consider KOH examination or fungal culture
- Scarring alopecias: Look for loss of follicular ostia
- Syphilis: Consider serologic testing in appropriate clinical context 2
Documentation for Monitoring
- Photograph affected areas
- Map hair loss distribution
- Document hair density measurements to establish baseline for comparison 1
Common Pitfalls to Avoid
- Failing to distinguish between active and stable disease (pull test helps)
- Missing associated autoimmune conditions that require separate management
- Overlooking psychological impact, which should be assessed and addressed
- Neglecting to rule out nutritional deficiencies that may exacerbate hair loss
Remember that while laboratory tests may help identify associated conditions, the diagnosis of alopecia areata is primarily clinical, with dermoscopy/trichoscopy being the most valuable confirmatory tool.