What laboratory tests should be ordered for a patient presenting with alopecia?

Laboratory Tests for Alopecia Evaluation

For patients presenting with alopecia, targeted laboratory testing should include complete blood count, ferritin levels, thyroid stimulating hormone, and vitamin D 25OH levels, with additional specialized tests based on clinical presentation. 1

Core Laboratory Panel for All Alopecia Patients

• Complete blood count (CBC): To assess for anemia and inflammatory markers
• Ferritin levels: To evaluate iron stores (even though studies show mixed results regarding iron deficiency in alopecia areata) 2, 1
• Thyroid function tests: TSH at minimum, as thyroid disorders can contribute to hair loss 1, 3
• Vitamin D 25OH levels: Multiple studies have shown association between vitamin D deficiency and alopecia areata 2

Additional Tests Based on Clinical Presentation

For suspected androgenetic alopecia:

• Androgen panel (total and free testosterone, DHEAS)
• Sex hormone binding globulin (SHBG)

For suspected alopecia areata:

• Antinuclear antibody (ANA) test
• C-reactive protein (CRP) - elevated levels have been observed in alopecia areata patients 2
• Consider newer hematological markers such as monocyte-lymphocyte ratio (MLR), monocyte-HDL ratio (MHR), and platelet-lymphocyte ratio (PLR) in specialized settings 4

For suspected infectious causes:

• Fungal culture (for suspected tinea capitis)
• KOH preparation of scalp scales

For suspected nutritional deficiencies:

• Zinc levels (studies show mixed results but zinc may play a role in some cases) 2
• Consider testing for vitamin B12, especially in vegetarian patients 3

Clinical Correlation and Testing Strategy

The laboratory evaluation should be guided by the clinical presentation:

1. Pattern of hair loss: Patchy (alopecia areata), diffuse (telogen effluvium), or patterned (androgenetic)
2. Presence of inflammation: Scaling, erythema (may indicate inflammatory conditions)
3. Hair shaft abnormalities: Exclamation mark hairs (alopecia areata), broken hairs (trichotillomania)
4. Associated symptoms: Fatigue (anemia, thyroid disease), weight changes (thyroid disease)

Important Considerations

• Laboratory testing should be targeted rather than ordering a comprehensive panel for all patients 1
• Despite multiple studies examining the relationship between iron deficiency and alopecia areata, results remain inconsistent, with only 2 of 8 studies supporting an association 2
• The majority of studies show a significant association between vitamin D deficiency and alopecia areata, making this an important test to include 2
• Consider scalp biopsy when physical examination findings are inconclusive or suggest scarring alopecia 1

Common Pitfalls to Avoid

• Ordering excessive laboratory tests without clinical correlation
• Failing to test for vitamin D, which has strong evidence supporting its association with alopecia areata
• Overlooking thyroid dysfunction, which can be a treatable cause of hair loss
• Neglecting to consider nutritional factors in vegetarian patients, who may have B12 deficiency contributing to anemia despite normal ferritin levels 3
• Focusing solely on laboratory results without correlating with clinical presentation and dermoscopic findings

By following this targeted laboratory approach based on clinical presentation, clinicians can efficiently diagnose the underlying cause of alopecia and develop appropriate treatment strategies.