Laboratory Evaluation for Hair Loss
Order androgen testing (total and free testosterone), along with iron studies (ferritin), vitamin D, zinc, thyroid profile (TSH), and prolactin to evaluate reversible causes of hair loss. 1
Mandatory Testing
Androgen Assessment
In all patients with female pattern hair loss (FPHL), assessment for androgen excess is mandatory 1:
- Total testosterone: Use high-quality assay, preferably liquid chromatography/mass spectrometry (LC/MS) or immunoassay with sample extraction and purification 1
- Free testosterone: Measure using equilibrium dialysis, ultracentrifugation, ammonium sulfate precipitation, or estimate using SHBG 1
- Avoid unreliable immunoassays without sample extraction 1
Clinical context: Most women with FPHL have normal androgen levels, so isolated FPHL with normal androgens should not be considered hyperandrogenism 1. However, testing is essential to identify the subset with treatable androgen excess.
Recommended Optional Testing
The following tests are optional but recommended to identify treatable conditions that impair hair regrowth 1:
Iron Studies
- Ferritin is the key marker 1
- Evidence is mixed: 29% of FPHL patients showed ferritin deficiency in one study 1, but other studies found no significant association 1
- Important caveat: The relationship between iron deficiency and FPHL remains uncertain, and iron supplementation in patients with low-normal ferritin (<70 μg/L) did not improve hair loss in controlled studies 1
- Despite equivocal evidence, checking ferritin is reasonable as it may identify a reversible contributor
Vitamin D
- Measure 25-hydroxyvitamin D 2
- 62% of FPHL patients had low vitamin D levels in one study 1
- Well-controlled studies are needed to establish whether correction improves hair growth 1
Zinc
- 15% of FPHL patients had low zinc levels 1
- Mean zinc levels were lower in women with FPHL versus controls 1
Thyroid Function
- TSH (thyroid-stimulating hormone) 1, 2
- Thyroid disorders don't appear significantly more common in FPHL than general population 1
- However, hypothyroidism can cause telogen effluvium and impair hair regrowth, making treatment difficult 1
- Particularly important in older women where subclinical hypothyroidism prevalence reaches 18% 1
Prolactin
- 7.2% of FPHL patients had elevated prolactin in one prospective series 1
- May be elevated secondary to hypothyroidism or hyperestrogenism 1
- The link between elevated prolactin and pattern hair loss remains unclear 1
Additional Testing Considerations
Complete Blood Count
- Recommended in some protocols 2 to assess for anemia and general health status
Tests NOT Routinely Needed
- Androstenedione, DHEA, DHEAS: Do not add much to detection of hyperandrogenism beyond total and free testosterone 1
- Baseline ECG or blood pressure: Not recommended when prescribing low-dose oral minoxidil unless specific precautions identified 3
Clinical Algorithm
- Start with androgen testing (total and free testosterone) in all patients
- Add thyroid function (TSH) given ease of testing and treatment implications
- Check ferritin despite mixed evidence, as it's easily correctable if low
- Consider vitamin D and zinc based on clinical suspicion and dietary history
- Add prolactin if menstrual irregularities or other suggestive symptoms present
Key pitfall: Don't over-interpret isolated low ferritin or vitamin D as the sole cause of hair loss, as correction may not improve FPHL 1. These should be treated as potential contributing factors that may impair response to primary hair loss treatments.