Laboratory Workup for Hair Loss
In all patients with hair loss, mandatory androgen assessment should be performed, with optional but recommended testing for vitamin D, iron studies, zinc, thyroid hormones, and prolactin 1.
Mandatory Testing
Androgen Assessment
All patients with female pattern hair loss (FPHL) require evaluation for androgen excess 1:
Total testosterone using high-quality assay:
- Preferably liquid chromatography/mass spectrometry (LC/MS)
- Alternative: immunoassay with sample extraction and purification
- Avoid standard immunoassays without extraction due to unreliability 1
Free testosterone measured by:
- Equilibrium dialysis (gold standard)
- Ultracentrifugation
- Ammonium sulfate precipitation
- Estimated using SHBG if direct measurement unavailable 1
Important caveat: Isolated FPHL with normal androgen levels should NOT be considered a sign of hyperandrogenism 1. Many patients with FPHL show no hormonal abnormalities despite symptoms 2.
Optional but Recommended Testing
The following tests help rule out conditions that may impair hair regrowth 1:
Iron Studies
- Serum ferritin is the key marker
- Evidence remains uncertain regarding the relationship between iron deficiency and FPHL 1
- No well-controlled studies demonstrate that correcting iron deficiency improves FPHL 1
- Despite this, testing is recommended to identify and treat deficiency
Vitamin D
- 25-hydroxyvitamin D levels
- Studies show 62% of FPHL patients have low vitamin D 1
- Relationship to hair loss requires further study
Zinc
- Mean zinc levels are lower in women with FPHL versus controls 1
- Approximately 15% of FPHL patients present with low zinc 1
Thyroid Function
- Thyroid profile (TSH at minimum)
- Rules out thyroid dysfunction affecting hair growth
Prolactin
- Elevated prolactin can contribute to hair loss
- Part of comprehensive endocrine evaluation
When Additional Testing is Needed
Complete blood count, ferritin, TSH, and vitamin D should be ordered in all patients with hair loss 3.
Additional testing depends on clinical presentation:
- Fungal culture if tinea capitis suspected
- Skin biopsy when diagnosis uncertain or scarring alopecia suspected 1, 3
- Lupus serology if systemic lupus erythematosus considered
- Syphilis serology in appropriate clinical context
Key Clinical Pitfalls
Don't over-interpret normal androgens: Sex hormone concentrations often don't correlate with clinical symptoms of hyperandrogenism in FPHL patients 2
Diagnosis is primarily clinical: Laboratory workup supplements but doesn't replace careful history and physical examination 1
Avoid routine autoimmune screening: The increased frequency of autoimmune disease in alopecia areata patients is insufficient to justify routine screening 4
Iron replacement without proven deficiency: No published studies demonstrate treatment response to iron replacement therapy in the absence of documented deficiency 4