Laboratory Testing for Hair Loss
Order serum ferritin, vitamin D, TSH, and zinc levels as your initial laboratory panel for most patients presenting with hair loss. 1
Core Laboratory Tests (First-Line)
These four tests form the foundation of your workup and should be ordered in nearly all patients with unexplained hair loss:
Serum ferritin is the single most important test, as iron deficiency is the world's most common nutritional deficiency and strongly associates with chronic diffuse telogen hair loss in women with both alopecia areata and androgenetic alopecia 1
Vitamin D levels should be checked universally, as 70% of alopecia areata patients are deficient (<20 ng/mL) compared to only 25% of controls, and lower levels correlate inversely with disease severity 2, 1
Thyroid stimulating hormone (TSH) must be checked to exclude thyroid disease, which is a common and 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, particularly those with resistant disease lasting more than 6 months 2, 1
Additional Testing Based on Clinical Presentation
For Women with Signs of Androgen Excess
If your patient presents with acne, hirsutism, or irregular menstrual periods, expand your workup:
Total testosterone or bioavailable/free testosterone and sex hormone binding globulin (SHBG) to assess for hyperandrogenism and possible polycystic ovary syndrome (PCOS) 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 assess for dyslipidemia that may accompany metabolic syndrome 1
When Diagnosis Remains Uncertain
Fungal culture is mandatory when tinea capitis is suspected, as incorrect diagnosis made on clinical grounds alone is the most common cause of treatment failure 2
Skin biopsy should be performed for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose clinically 2
Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 2
Serology for syphilis when secondary syphilis is suspected (presents with patchy "moth-eaten" hair loss) 2
Clinical Context Matters
Most cases of alopecia areata are diagnosed clinically without laboratory workup. 2 Laboratory testing is indicated when:
- The diagnosis is uncertain or the presentation is atypical 2
- Other conditions in the differential diagnosis need to be ruled out 2
- Diffuse alopecia areata is suspected, which may require biopsy for definitive diagnosis 2
Critical Pitfalls to Avoid
Do not order excessive laboratory tests when the diagnosis is clinically evident, as alopecia areata is typically diagnosed through pattern recognition using dermoscopy to identify yellow dots and exclamation mark hairs 1
Do not overlook the psychological impact of hair loss, which may warrant assessment for anxiety and depression regardless of laboratory findings, as patients with moderate to severe hair loss are more likely to have accompanying anxiety, depression, and lower work productivity 1, 3
Do not forget thyroid peroxidase (TPO) antibody testing if biochemical hypothyroidism is confirmed (high TSH and low free T4) 2
Dermoscopy as a Diagnostic Tool
Before ordering extensive laboratory tests, consider using dermoscopy as the single most useful non-invasive tool to differentiate diffuse alopecia areata, telogen effluvium, and androgenetic alopecia by looking for yellow dots, exclamation mark hairs, and cadaverized hairs 2