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 and diagnosis should be made clinically, but when hair loss is diffuse, atypical, or the diagnosis is uncertain, targeted laboratory testing should include serum ferritin, vitamin D, TSH, and zinc levels. 1

When to Order Laboratory Tests

Avoid routine testing when the diagnosis is clinically clear – the British Journal of Dermatology explicitly states that investigations are unnecessary in most cases of alopecia areata, as the diagnosis is usually made clinically. 1 However, laboratory workup becomes essential when:

• The presentation is atypical or diagnosis uncertain 1
• Diffuse alopecia areata is suspected, which may be challenging to diagnose 1
• Other conditions in the differential diagnosis need exclusion 1
• Signs of systemic disease or hormonal abnormalities are present 1

Core Laboratory Panel for Hair Loss

Nutritional Deficiencies (Most Common Treatable Causes)

• Serum ferritin – Iron deficiency is the most common nutritional deficiency worldwide and a sign of chronic diffuse telogen hair loss, with levels consistently lower in women with both alopecia areata and androgenetic alopecia 1

• Vitamin D (25-OH) – Deficiency (<20 ng/mL or <50 nmol/L) shows strong association with hair loss, with 70% of alopecia areata patients deficient versus only 25% of controls, and lower levels correlate inversely with disease severity 1, 2

• Serum zinc – Serves as a cofactor for multiple enzymes involved in hair follicle function, with levels tending to be lower in patients with alopecia areata 1

• Folate – Deficiency may contribute to hair loss and should be assessed 1

Thyroid Function

• TSH (thyroid stimulating hormone) – Essential to rule out thyroid disease, which can cause hair loss; high TSH with low free T4 indicates biochemical hypothyroidism 1, 2

• Thyroid peroxidase (TPO) antibodies – Warranted if biochemical hypothyroidism is confirmed, given the association between alopecia areata and autoimmune thyroid disease 1

Hormonal Evaluation (When Androgen Excess is Suspected)

The American Academy of Family Physicians recommends the following only in women with signs of androgen excess such as acne, hirsutism, and irregular periods: 1

• Total testosterone or bioavailable/free testosterone levels 1
• Sex hormone binding globulin (SHBG) 1
• Prolactin level if hyperprolactinemia is suspected 1
• Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected (associated with PCOS) 1
• Fasting lipid and lipoprotein levels to evaluate for dyslipidemia 1

Additional Testing for Specific Differential Diagnoses

When Infection is Suspected

• Fungal culture – Recommended when tinea capitis (scalp ringworm) is suspected, as it requires oral antifungal therapy and signs may be subtle 1

When Systemic Disease is Suspected

• Serology for lupus erythematosus – When systemic lupus is in the differential diagnosis, as it can cause both scarring and non-scarring alopecia 1

• Serology for syphilis – When secondary syphilis is suspected, which presents with patchy "moth-eaten" hair loss 1

When Diagnosis Remains Uncertain

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

Common Pitfalls to Avoid

• Ordering excessive laboratory tests when the diagnosis is clinically evident – This wastes resources and delays appropriate treatment 1

• Failing to use dermoscopy – This non-invasive tool can provide valuable diagnostic information, looking for yellow dots, exclamation mark hairs, and cadaverized hairs in alopecia areata 1, 3

• Overlooking the psychological impact – Assessment for anxiety and depression may be warranted, as hair loss can be devastating to patients 1, 3

Algorithmic Approach

1. Clinical diagnosis first – Use history, physical examination, and dermoscopy 1
2. If diagnosis is clear (typical alopecia areata) – No laboratory testing needed 1
3. If diffuse hair loss or uncertain diagnosis – Order core panel: ferritin, vitamin D, TSH, zinc, folate 1, 2
4. If signs of androgen excess present – Add hormonal evaluation (testosterone, SHBG, prolactin, glucose tolerance test) 1
5. If specific conditions suspected – Add targeted tests (fungal culture, lupus serology, syphilis serology) 1
6. If diagnosis still uncertain – Proceed to scalp biopsy 1, 3