Laboratory Testing for Hair Thinning
Order serum ferritin, vitamin D, TSH, and zinc levels as your initial laboratory panel for most patients presenting with hair thinning. 1
Core Laboratory Tests (Order These First)
Serum ferritin is the single most important test, as iron deficiency is the world's most common nutritional deficiency and strongly associates with chronic diffuse telogen hair loss, with lower levels found in both alopecia areata and androgenetic alopecia patients. 1
Vitamin D (25-OH) should be checked in all patients, as 70% of alopecia areata patients have deficiency (<20 ng/mL) compared to 25% of controls, with lower levels correlating inversely with disease severity. 2, 1
Thyroid stimulating hormone (TSH) must be checked to exclude thyroid disease, a common reversible cause of hair loss. 2, 1 If TSH is elevated with low free T4 (biochemical hypothyroidism), add thyroid peroxidase (TPO) antibody testing. 2
Serum zinc should be measured, as zinc serves as a cofactor for multiple enzymes in hair follicle function and tends to be lower in alopecia areata patients, particularly those with resistant disease >6 months duration. 2, 1
Additional Testing Based on Clinical Presentation
When Signs of Androgen Excess Are Present
If the patient has acne, hirsutism, or irregular menstrual periods, order: 1
- Total testosterone or bioavailable/free testosterone
- Sex hormone binding globulin (SHBG)
- Prolactin level if hyperprolactinemia is suspected 2
- Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected 2
- Fasting lipid panel to assess for dyslipidemia accompanying metabolic syndrome 2
When Specific Diagnoses Are Suspected
Fungal culture is mandatory when tinea capitis is suspected—this is the most common cause of treatment failure when diagnosis is made on clinical grounds alone. 2
Serology for lupus erythematosus when systemic lupus is in the differential diagnosis. 2
Serology for syphilis when secondary syphilis is suspected (presents with patchy "moth-eaten" hair loss). 2
Scalp biopsy is reserved for difficult cases, early scarring alopecia, or diffuse alopecia areata that is diagnostically challenging. 2
Critical Pitfalls to Avoid
Do not order excessive laboratory tests when the diagnosis is clinically evident, as alopecia areata is typically diagnosed through pattern recognition using dermoscopy (looking for yellow dots, exclamation mark hairs, and cadaverized hairs). 2, 1
Do not delay treatment for suspected nutritional deficiencies if the patient presents with rapid weight loss, poor dietary intake, or vomiting—initiate treatment immediately without waiting for blood results. 1
Do not overlook the psychological impact of hair loss, which may warrant assessment for anxiety and depression regardless of laboratory findings, as patients with moderate to severe hair loss have significantly lower quality-of-life scores. 1
Do not forget dermoscopy as a non-invasive diagnostic tool—it is the single most useful tool to differentiate diffuse alopecia areata, telogen effluvium, and androgenetic alopecia before ordering extensive laboratory workups. 2
When Laboratory Testing Is NOT Necessary
Investigations are unnecessary in most cases of alopecia areata when the diagnosis is clinically evident with characteristic dermoscopic findings (yellow dots and exclamation mark hairs). 2 Laboratory tests should only be considered when the diagnosis is uncertain, presentation is atypical, or other conditions in the differential diagnosis need to be ruled out. 2