What laboratory tests are recommended for patients presenting with hair loss?

Laboratory Testing for Hair Loss

In most cases of clinically evident alopecia areata, laboratory investigations are unnecessary, but when hair loss is diffuse, uncertain, or atypical, check serum ferritin (target ≥60 ng/mL), vitamin D (target ≥20 ng/mL), TSH, and zinc levels. 1

Core Laboratory Panel for Hair Loss

The following tests should be ordered based on clinical presentation:

First-Line Tests (Order for Most Patients with Diffuse Hair Loss)

• Serum ferritin is the single most important nutritional test, as iron deficiency is the most common nutritional deficiency worldwide and a sign of chronic diffuse telogen hair loss, with optimal levels ≥60 ng/mL needed for hair growth 1, 2

• Vitamin D (25-OH) should be checked, as 70% of alopecia areata patients have deficiency (<20 ng/mL) versus 25% of controls, with lower levels correlating inversely with disease severity 1, 2

• Thyroid stimulating hormone (TSH) is essential to rule out thyroid disease, which commonly causes hair loss 1, 3

• Serum zinc tends to be lower in alopecia areata patients, particularly those with resistant disease >6 months duration 1

Conditional Tests (Order Only When Clinically Indicated)

• Free testosterone, total testosterone, and SHBG should only be checked in women with signs of androgen excess such as acne, hirsutism, or irregular periods 1, 3

• Prolactin level if hyperprolactinemia is suspected 1

• Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected 1

• Fasting lipid panel to evaluate for dyslipidemia if clinically indicated 1

• Thyroid peroxidase (TPO) antibodies only if biochemical hypothyroidism is confirmed (high TSH, low free T4) 1

Diagnosis-Specific Testing

When Alopecia Areata is Clinically Evident

• No laboratory workup is needed in most cases, as the diagnosis is made clinically by identifying patchy hair loss with exclamation mark hairs 1, 3

• Laboratory tests should only be considered when the diagnosis is uncertain, presentation is atypical, or other conditions need to be ruled out 1

When Infectious or Systemic Disease is Suspected

• Fungal culture is mandatory when tinea capitis is suspected, particularly with scalp inflammation or scaling 1, 3

• Skin biopsy is recommended for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose 1, 3

• 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

Common Pitfalls to Avoid

• Avoid ordering excessive laboratory tests when the diagnosis is clinically evident, particularly in straightforward alopecia areata cases 1, 3

• Don't overlook dermoscopy as a non-invasive diagnostic tool that can identify yellow dots, exclamation mark hairs, and cadaverized hairs in alopecia areata 1

• Don't forget to assess psychological impact, as alopecia can cause considerable psychological and social disability warranting evaluation for anxiety and depression 1

• Remember that 34-50% of alopecia areata patients recover within one year without treatment, making the tendency to spontaneous remission an important consideration before ordering extensive workups 1, 3