Laboratory Workup for Hair Loss in Patients on GLP-1 Receptor Agonists
Order a comprehensive metabolic panel including: thyroid function (TSH), iron studies (ferritin), vitamin D (25-hydroxyvitamin D), zinc level, total and free testosterone (using LC/MS or high-quality assay with SHBG), and prolactin. 1
Core Laboratory Tests
The following labs should be obtained based on guideline recommendations for evaluating hair loss, which applies to GLP-1-associated alopecia:
Essential Hormone Panel
- Thyroid function (TSH): Hypothyroidism can cause telogen effluvium and impair hair regrowth, even when subclinical 1
- Prolactin: Elevated in 7.2% of hair loss patients in prospective studies, with 1.8% having prolactinomas 1
Androgen Assessment
- Total testosterone: Use LC/MS or immunoassay with extraction/purification (not direct immunoassay, which is inaccurate) 1
- Free testosterone: Measured by equilibrium dialysis, ultracentrifugation, or ammonium sulfate precipitation; alternatively calculate using SHBG with accurate total testosterone 1
- SHBG: Allows calculation of free testosterone when direct measurement unavailable 1
Nutritional Deficiencies
- Ferritin: 29% of hair loss patients show deficiency, though the causal relationship remains uncertain 1
- Vitamin D (25-hydroxyvitamin D): Low in 62% of hair loss patients in Vancouver study 1
- Zinc: Deficient in 15% of hair loss patients; mean levels lower in affected women versus controls 1
GLP-1-Specific Context
Recent evidence shows semaglutide and tirzepatide have the highest incidence of hair loss among GLP-1 RAs, with telogen effluvium and androgenetic alopecia being the predominant subtypes 2. The mechanism appears related to:
- Rapid weight loss: Particularly associated with tirzepatide-induced telogen effluvium 2
- Dose-dependent effect: Semaglutide doses <2mg weekly rarely implicated; higher obesity-treatment doses more commonly associated 2
- Female predominance: Women disproportionately affected 2, 3
Important Nuances
The evidence for nutritional supplementation improving hair regrowth is weak. Iron supplementation in patients with ferritin <70 mg/L did not improve hair loss in controlled studies 1. However, correcting these deficiencies is still recommended as they may impair regrowth capacity 1.
Androgen testing is critical even though GLP-1-associated hair loss is not primarily androgenic. This distinguishes between drug-induced telogen effluvium (reversible) versus underlying androgenetic alopecia that may be unmasked or worsened by rapid weight loss 1.
Common Pitfalls to Avoid
- Do not use direct radioimmunoassay or chemiluminescent immunoassay for testosterone - these are notoriously inaccurate in women 1
- Do not skip nutritional testing - even if deficiencies don't cause the hair loss, they prevent optimal regrowth 1
- Do not assume all GLP-1 RAs carry equal risk - semaglutide shows disproportionate reporting for alopecia (adjusted OR 1.23), while dulaglutide and some others show lower risk 4