Laboratory Testing for Hair Loss
Order serum ferritin, vitamin D, TSH, and zinc levels as the initial laboratory panel for all patients presenting with hair loss. 1
Core Laboratory Tests (Order These First)
The following four tests form the essential baseline workup and should be obtained in virtually all patients with 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, with lower levels found in both alopecia areata and androgenetic alopecia patients 1
Vitamin D levels should be checked universally, as 70% of alopecia areata patients have deficiency (<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 measured to exclude thyroid disease, which represents a common and reversible cause of hair loss 2, 1
Serum zinc levels should be obtained, 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 >6 months duration 2, 1
Additional Testing Based on Clinical Presentation
When Signs of Androgen Excess Are Present
If the patient exhibits acne, hirsutism, or irregular menstrual periods, expand testing to include:
Total testosterone or bioavailable/free testosterone and sex hormone binding globulin (SHBG) to assess for hyperandrogenism and polycystic ovary syndrome (PCOS) 2, 1
Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected, as these conditions associate with PCOS-related hair loss 2, 1
Fasting lipid panel to evaluate for dyslipidemia that may accompany metabolic syndrome 2, 1
When Specific Differential Diagnoses Are Suspected
Fungal culture is mandatory when tinea capitis (scalp ringworm) is suspected, as incorrect diagnosis made on clinical grounds alone is the most common cause of treatment failure 2, 3
Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 2, 3
Serology for syphilis when secondary syphilis is suspected (presents with patchy "moth-eaten" hair loss) 2
Thyroid peroxidase (TPO) antibody testing is warranted if biochemical hypothyroidism is confirmed (high TSH and low free T4) 2
When Laboratory Testing Is NOT Needed
Do not order laboratory tests when alopecia areata is clinically evident with characteristic features. 2, 1
The diagnosis of alopecia areata is typically made clinically without laboratory workup in most cases, characterized by:
- Patchy, non-scarring hair loss with well-demarcated borders 2
- Exclamation mark hairs (short broken hairs around expanding patches) which are pathognomonic 2
- Yellow dots, cadaverized hairs, and black dots on dermoscopy 2
Laboratory testing should only be considered when:
- The diagnosis is uncertain or presentation is atypical 2
- Other conditions in the differential diagnosis need to be ruled out 2
- Diffuse alopecia areata is suspected, which may be diagnostically challenging 2
Critical Pitfalls to Avoid
Avoid ordering excessive laboratory tests when the diagnosis is clinically evident, as this wastes resources and delays appropriate treatment 2, 1
Do not overlook dermoscopy as a non-invasive diagnostic tool that can differentiate diffuse alopecia areata, telogen effluvium, and androgenetic alopecia without laboratory testing 2
Consider scalp biopsy for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose, rather than ordering more laboratory tests 2
Do not fail to assess the psychological impact of hair loss, which may warrant evaluation for anxiety and depression regardless of laboratory findings, as alopecia can cause considerable psychological and social disability 2, 1
Remember that 34-50% of alopecia areata patients recover within one year without treatment, making observation a reasonable option for limited disease rather than extensive workup 2