What lab workup is recommended for a patient presenting with hair loss to determine the underlying cause and guide treatment?

Laboratory Workup for Hair Loss

In most cases of clinically evident alopecia areata, laboratory investigations are unnecessary and the diagnosis should be made clinically; however, targeted laboratory testing is indicated when the diagnosis is uncertain, presentation is atypical, or when specific underlying conditions need to be excluded. 1

Initial Diagnostic Strategy

The approach to laboratory testing depends on clinical presentation and should avoid excessive testing when the diagnosis is clear 1:

• Clinically evident alopecia areata (patchy loss with exclamation mark hairs on dermoscopy) requires no laboratory workup 1, 2
• Uncertain diagnosis or atypical presentations warrant targeted testing based on differential diagnosis 1
• Diffuse hair loss patterns require more comprehensive evaluation to distinguish between telogen effluvium, androgenetic alopecia, and diffuse alopecia areata 1

Essential Laboratory Tests

Nutritional Deficiency Panel

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 1:

• Optimal level for hair growth is ≥60 ng/mL 2
• Lower levels are found in women with both alopecia areata and androgenetic alopecia 1

Vitamin D (25-OH) should be checked in all patients with hair loss 3:

• Deficiency defined as <20 ng/mL or <50 nmol/L 1
• 70% of alopecia areata patients are deficient versus 25% of controls 1
• Lower levels correlate inversely with disease severity 1

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

• Zinc serves as a cofactor for multiple enzymes involved in hair follicle function 1

Thyroid Function Tests

TSH and free T4 should be checked to rule out thyroid disease, which commonly causes hair loss 1, 2:

• High TSH and low free T4 indicate biochemical hypothyroidism 1
• If hypothyroidism is confirmed, thyroid peroxidase (TPO) antibody testing is warranted 1
• Alopecia areata associates with other autoimmune diseases including thyroid disease 1

Hormone Testing (Selective)

Total testosterone, free testosterone, and SHBG should only be checked in women with signs of androgen excess 1, 2:

• Clinical signs include acne, hirsutism, and irregular periods 1
• Consider testing for polycystic ovary syndrome (PCOS) in this context 1

Prolactin level if hyperprolactinemia is suspected as a contributor to hair loss 1

Condition-Specific Testing

When Infectious Causes Are Suspected

Fungal culture is mandatory when tinea capitis is suspected based on scalp inflammation, scaling, or erythematous patches 1, 2:

• This is the most common cause of treatment failure when diagnosis is made on clinical grounds alone 1

When Systemic Disease Is Suspected

Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 1:

• Lupus 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 is recommended for 1, 2:

• Difficult cases where diagnosis is uncertain
• Early scarring alopecia
• Diffuse alopecia areata that is challenging to diagnose clinically
• Any suspected scarring alopecia pattern 4

Additional Metabolic Testing (Context-Dependent)

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

Fasting lipid and lipoprotein levels to evaluate for dyslipidemia that may be related to hair loss 1

Common Pitfalls to Avoid

• Ordering excessive laboratory tests when the diagnosis is clinically evident wastes resources and delays appropriate management 1, 2
• Ordering extensive autoimmune panels in straightforward alopecia areata cases is unnecessary 2
• Failing to use dermoscopy as a non-invasive diagnostic tool that can provide valuable information and potentially eliminate the need for laboratory testing 1
• Overlooking the psychological impact of alopecia, which may warrant assessment for anxiety and depression rather than additional laboratory tests 1
• Missing trichotillomania in the differential, where broken hairs remain firmly anchored and laboratory testing will be unrevealing 2

Practical Algorithm

1. Perform dermoscopy first looking for yellow dots, exclamation mark hairs, and cadaverized hairs 1
2. If characteristic features of alopecia areata are present, diagnose clinically without laboratory workup 1, 2
3. If diffuse pattern or diagnosis uncertain, obtain: serum ferritin, vitamin D, TSH, and zinc 1, 3
4. If scalp inflammation/scaling present, obtain fungal culture 1, 2
5. If signs of androgen excess, add testosterone panel and consider PCOS workup 1
6. If systemic disease suspected, add targeted serology (lupus, syphilis) 1
7. If diagnosis still uncertain after above, proceed to scalp biopsy 1, 2