What lab tests are recommended for diagnosing hair loss?

Laboratory Testing for Hair Loss

In most cases of clinically evident alopecia areata, laboratory investigations are unnecessary, but when the diagnosis is uncertain or other causes are suspected, targeted testing should include serum ferritin, vitamin D, TSH, and consideration of fungal culture, skin biopsy, or serologies based on clinical presentation. 1, 2

When Laboratory Testing is NOT Needed

• Investigations are unnecessary in most cases of alopecia areata when the diagnosis is clinically straightforward, as the condition is typically diagnosed by characteristic patchy hair loss with exclamation mark hairs at the margins of expanding patches 1
• Routine screening for autoimmune diseases in alopecia areata patients is not justified despite the increased frequency of autoimmune conditions in this population 1

Essential Laboratory Tests When Diagnosis is Uncertain

First-Line Nutritional and Hormonal Screening

• Serum ferritin should be checked in all patients with hair loss, as iron deficiency is the most common nutritional deficiency worldwide and a marker of chronic diffuse telogen hair loss, with levels consistently lower in women with alopecia areata and androgenetic alopecia 2
• Vitamin D levels (25-hydroxyvitamin D) should be measured, as deficiency (<20 ng/mL or <50 nmol/L) shows an inverse correlation with disease severity, with 70% prevalence in alopecia areata patients versus 25% in controls 2
• Thyroid stimulating hormone (TSH) must be checked to rule out thyroid disease, which is a common reversible cause of hair loss 2
• If TSH is elevated with low free T4 indicating biochemical hypothyroidism, thyroid peroxidase (TPO) antibody testing is warranted 2
• Serum zinc levels should be considered, as zinc serves as a cofactor for multiple enzymes involved in hair follicle function and tends to be lower in alopecia areata patients 2

Hormonal Testing in Women with Signs of Androgen Excess

• Total testosterone or bioavailable/free testosterone levels and sex hormone binding globulin (SHBG) should be tested in women presenting with acne, hirsutism, and irregular periods alongside hair loss 2
• Consider screening for polycystic ovary syndrome (PCOS) in women with signs of androgen excess 2
• Check prolactin levels if hyperprolactinemia is suspected as a contributing factor 2
• Perform a two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected 2
• Assess fasting lipid and lipoprotein levels to evaluate for dyslipidemia that may be related to hair loss 2

Diagnostic Tests for Specific Differential Diagnoses

When Infectious or Inflammatory Causes are Suspected

• Fungal culture is indicated when tinea capitis is suspected, particularly if the scalp shows inflammation or scaling, even if subtle 1, 2
• Skin biopsy is recommended for difficult cases, including early scarring alopecia, diffuse alopecia areata that is challenging to diagnose clinically, or when the diagnosis remains uncertain after initial evaluation 1, 2
• Serology for lupus erythematosus should be performed when systemic lupus is in the differential diagnosis, particularly if there are other systemic symptoms or signs of scarring alopecia 1, 2
• Serology for syphilis is indicated when secondary syphilis is suspected based on clinical presentation 1, 2

Key Differential Diagnoses Requiring Different Testing Approaches

• Trichotillomania (compulsive hair pulling) is distinguished clinically by incomplete hair loss with firmly anchored broken hairs remaining in anagen phase, unlike exclamation mark hairs in alopecia areata 1
• Tinea capitis requires fungal culture and shows scalp inflammation with scaling 1
• Telogen effluvium and anagen effluvium (drug-induced) may require careful medication history rather than extensive laboratory testing 1
• Early scarring alopecia necessitates skin biopsy for definitive diagnosis 1

Common Pitfalls to Avoid

• Avoid ordering excessive laboratory tests when the diagnosis is clinically evident, as this increases costs without improving outcomes 2
• Do not overlook dermoscopy as a non-invasive diagnostic tool that can identify yellow dots, exclamation mark hairs, and cadaverized hairs characteristic of alopecia areata 2
• Failing to assess the psychological impact of hair loss is a critical oversight, as alopecia can be devastating and may warrant evaluation for anxiety and depression 1, 3
• Remember that folate deficiency may also contribute to hair loss and should be considered in the nutritional assessment 2