What tests are used to diagnose hair loss?

Diagnostic Testing for Hair Loss

Most cases of hair loss can be diagnosed clinically without laboratory testing, but when tests are needed, prioritize TSH, serum ferritin, vitamin D, and zinc levels based on clinical presentation. 1

When Laboratory Testing is NOT Needed

• Skip laboratory workup when alopecia areata is clinically evident with characteristic exclamation mark hairs and patchy non-scarring hair loss 1
• Avoid ordering extensive laboratory panels when the diagnosis is clear from clinical examination, as this wastes resources and delays appropriate management 2
• Most cases of androgenetic alopecia (pattern hair loss) are diagnosed by recognizable patterns on examination and do not require testing 3

When Laboratory Testing IS Indicated

Laboratory tests should be ordered when: 1

• The diagnosis is uncertain or presentation is atypical
• Diffuse alopecia areata is suspected (may require biopsy)
• Other conditions in the differential diagnosis need to be ruled out
• Signs of systemic disease or hormonal abnormalities are present

Essential Laboratory Tests by Clinical Scenario

For Diffuse Hair Loss (Most Common Scenario)

The British Journal of Dermatology recommends this targeted approach: 1, 4

• Thyroid stimulating hormone (TSH) - Rule out thyroid disease, which commonly causes hair loss 1

  • If TSH is elevated with low free T4, add thyroid peroxidase (TPO) antibody testing 1

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

• Vitamin D (25-OH) - 70% of alopecia areata patients have deficiency (<20 ng/mL) versus 25% of controls, with lower levels correlating 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

For Women with Signs of Androgen Excess

When acne, hirsutism, or irregular periods are present: 1

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

For Suspected Infectious or Systemic Causes

• Fungal culture - When tinea capitis (scalp ringworm) is suspected with scalp inflammation and scaling 1, 5
• Serology for lupus erythematosus - When systemic lupus is in the differential diagnosis with joint pain, rash, or photosensitivity 1, 5
• Serology for syphilis - When secondary syphilis is suspected with patchy "moth-eaten" hair loss 1, 5

Non-Laboratory Diagnostic Tools

Dermoscopy (First-Line Non-Invasive Tool)

Dermoscopy aids diagnosis of alopecia areata by identifying: 1

• Yellow dots
• Exclamation mark hairs (short broken hairs with tapered bases indicating active disease)
• Cadaverized hairs

This tool is routinely used to facilitate diagnosis, stage severity, and monitor disease progression and treatment response 6

Skin Biopsy (When Needed)

Scalp biopsy is recommended for: 1

• Difficult cases where diagnosis remains uncertain
• Early scarring alopecia
• Diffuse alopecia areata that is challenging to diagnose clinically
• All cases of cicatricial (scarring) alopecia 4

Critical pitfall: Biopsies must be processed and interpreted correctly to be useful 7

Clinical Examination Priorities Over Testing

Before ordering any tests, perform these clinical assessments: 5, 2

• Determine if scarring or non-scarring - This fundamentally directs all subsequent decisions 2
• Assess hair pull test - Determines if hair can be easily pulled out 5
• Look for exclamation mark hairs - Indicates active alopecia areata 5, 2
• Examine for incomplete patches with firmly anchored broken hairs - Suggests trichotillomania, not alopecia areata 2
• Check for scalp inflammation or scaling - Raises concern for tinea capitis or scarring alopecia 2

Common Pitfalls to Avoid

• Do not order excessive laboratory tests when diagnosis is clinically evident - Alopecia areata is typically diagnosed clinically without workup 1, 2
• Do not confuse trichotillomania with alopecia areata - Broken hairs in trichotillomania remain firmly anchored in anagen phase, unlike exclamation mark hairs 2
• Do not overlook dermoscopy as a valuable non-invasive diagnostic tool that can provide immediate information 1
• Do not forget to assess psychological impact - Hair loss may cause considerable psychological and social disability warranting assessment for anxiety and depression 1, 2