What laboratory tests should be ordered for a patient with excessive hair shedding?

Laboratory Testing for Excessive Hair Shedding

For patients with excessive hair shedding, order the following core laboratory panel: thyroid profile (TSH), iron studies (ferritin, hemoglobin/CBC), vitamin D 25-OH, and in women, androgen testing (total testosterone by LC/MS and free testosterone or SHBG). 1

Essential Laboratory Tests

First-Tier Testing (Order for All Patients)

Thyroid Function:

• TSH to screen for hypothyroidism
• While thyroid disorders aren't significantly more common in hair loss patients than the general population, subclinical hypothyroidism can cause telogen effluvium and impair hair regrowth 1

Iron Studies:

• Ferritin level (most important marker)
• Complete blood count with hemoglobin
• Important caveat: The relationship between iron deficiency and hair loss remains controversial. Studies show conflicting results—some found 29-44% of hair loss patients had low ferritin, while others found no significant difference from controls 1. However, hemoglobin specifically correlates positively with anagen hair ratios in female patients 2
• Iron supplementation in patients with low-normal ferritin (<70 mg/L) has not been shown to improve hair loss 1

Vitamin D:

• 25-hydroxyvitamin D level
• Studies show 62-87% of hair loss patients have low vitamin D levels 1

Second-Tier Testing (For Women with Hair Loss)

Androgen Panel:

• Total testosterone using high-quality assay (preferably LC/MS or immunoassay with extraction/purification) 1
• Free testosterone (via equilibrium dialysis, ultracentrifugation, or calculated using SHBG) 1
• Free testosterone is more sensitive than total testosterone for detecting androgen excess 1
• Avoid direct immunoassays for free testosterone—they are notoriously inaccurate 1

Additional Hormones:

• Prolactin (7.2% of female pattern hair loss patients had elevated prolactin in one study) 1
• DHEAS, androstenedione (less useful—don't add much to detection of hyperandrogenism) 1

Optional Testing (Lower Yield)

Zinc:

• Only 4.5-15% of patients show deficiency 1, 2
• No proven correlation with hair regrowth outcomes

Vitamin B12 and Folate:

• Very low deficiency rates (1.5% and 2.5% respectively) 2
• Consider only if other risk factors present

Clinical Algorithm

1. Start with history and scalp examination to determine if hair loss is diffuse vs. focal, scarring vs. non-scarring 1

2. Order core panel for all patients: TSH, ferritin, CBC, vitamin D

3. Add androgen testing for women presenting with:

   • Female pattern hair loss (central/frontal thinning)
   • Signs of hyperandrogenism (hirsutism, acne, menstrual irregularities)
   • Note: 40% of women report androgenic symptoms, but hormone levels often don't correlate with symptoms 3

4. Consider scalp biopsy if diagnosis unclear or to differentiate between conditions (e.g., female pattern hair loss vs. chronic telogen effluvium) 1

Key Pitfalls to Avoid

• Don't rely on standard testosterone immunoassays—they're unreliable in women. Insist on LC/MS or extracted samples 1
• Don't over-interpret low-normal ferritin—supplementation hasn't proven beneficial, and iron deficiency is common in the general premenopausal population 1
• Don't order extensive micronutrient panels routinely—zinc, B12, and folate deficiencies are rare and not clearly linked to treatment outcomes 2
• Hemoglobin is the only marker with proven positive correlation to anagen hair ratios in telogen effluvium patients 2

The evidence shows that while multiple nutritional and hormonal abnormalities are found in hair loss patients, only thyroid dysfunction, anemia, and androgen excess have clear clinical relevance for treatment decisions 1. The relationship between correcting other deficiencies and improving hair growth remains unproven 1.