Laboratory Testing for Hair Loss
For most patients with hair loss, order serum ferritin, vitamin D (25-hydroxyvitamin D), TSH, and zinc levels as your initial laboratory panel. 1
Core Laboratory Tests
First-Line Testing (Order for All Patients)
Serum ferritin is the most important test, as iron deficiency is the world's most common nutritional deficiency and strongly associated with chronic diffuse telogen hair loss, with lower levels found in women with both alopecia areata and androgenetic alopecia 1
Vitamin D (25-hydroxyvitamin D) should be checked in all patients, as 70% of alopecia areata patients have deficiency (<20 ng/mL or <50 nmol/L) versus only 25% of controls, with lower levels correlating inversely with disease severity 1
Thyroid stimulating hormone (TSH) must be checked to exclude thyroid disease, which is a common reversible cause of hair loss 1
Serum zinc levels should be measured, as zinc serves as a cofactor for multiple enzymes involved in hair follicle function and tends to be lower in alopecia areata patients 1
Additional Testing Based on Clinical Presentation
When Signs of Androgen Excess Are Present
If the patient has acne, hirsutism, or irregular menstrual periods, expand your workup to include:
Total testosterone or bioavailable/free testosterone and sex hormone binding globulin (SHBG) to evaluate for hyperandrogenism 1
Prolactin level if hyperprolactinemia is suspected 1
Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected, as these conditions associate with PCOS-related hair loss 1
Fasting lipid panel to evaluate for dyslipidemia that may accompany metabolic syndrome 1
When Thyroid Disease Is Confirmed
- Thyroid peroxidase (TPO) antibody testing is warranted if biochemical hypothyroidism is confirmed (high TSH and low free T4) 1
When Specific Diagnoses Are Suspected
Fungal culture is mandatory when tinea capitis is suspected, as this requires oral antifungal therapy 1, 2
Skin biopsy should be performed for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose clinically 1, 2
Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 1
Serology for syphilis when secondary syphilis is suspected (presents with patchy "moth-eaten" hair loss) 1
Critical Pitfalls to Avoid
Do not order excessive laboratory tests when the diagnosis is clinically evident, as alopecia areata is typically diagnosed clinically through pattern recognition (patchy hair loss with exclamation mark hairs) 1, 2
Do not delay treatment for thiamine deficiency if the patient presents with rapid weight loss, poor dietary intake, vomiting, or symptoms of neuropathy—initiate treatment immediately without waiting for blood results 3
Do not confuse normal ferritin with optimal ferritin, as some experts believe ferritin levels should be higher than standard reference ranges for optimal hair growth, though this remains controversial 4
Do not overlook the psychological impact of hair loss, which may warrant assessment for anxiety and depression regardless of laboratory findings 1, 2
When Laboratory Testing Is NOT Needed
Investigations are unnecessary in most cases of alopecia areata when the diagnosis is clinically evident with characteristic patchy hair loss and exclamation mark hairs 1
Laboratory tests should only be considered when the diagnosis is uncertain, presentation is atypical, or other conditions in the differential diagnosis need to be ruled out 1