Laboratory Evaluation for Hair Loss in Women
Order a focused panel including complete blood count (CBC), serum ferritin, thyroid-stimulating hormone (TSH), and vitamin D levels as your baseline workup for any woman presenting with hair loss. 1
Essential First-Line Laboratory Tests
The following tests should be ordered initially for all women with hair loss:
Serum ferritin is the single most important test for iron stores, with ferritin ≤15 μg/L confirming iron deficiency with 98% specificity in premenopausal women 1. Iron deficiency is the most common nutritional deficiency worldwide and a sign of chronic diffuse telogen hair loss 2.
Complete blood count (CBC) to evaluate for anemia, which commonly accompanies hair loss 1, 3.
Thyroid-stimulating hormone (TSH) to rule out thyroid disease, which can cause hair loss 2, 3. If TSH is elevated with low free T4 indicating biochemical hypothyroidism, thyroid peroxidase (TPO) antibody testing is warranted 2.
Vitamin D levels should be checked, as deficiency (<20 ng/mL or <50 nmol/L) shows strong association with hair loss, with 70% of alopecia areata patients being deficient versus 25% of controls, and lower levels correlate inversely with disease severity 2.
Serum zinc levels tend to be lower in patients with alopecia areata, particularly those with resistant disease >6 months duration 2.
Additional Tests When Androgen Excess is Suspected
If clinical signs suggest hyperandrogenism (acne, hirsutism, irregular periods, male-pattern distribution of hair loss), expand your workup:
Total testosterone or bioavailable/free testosterone along with sex hormone binding globulin (SHBG) levels 2, 3.
Dehydroepiandrosterone sulfate (DHEAS) to evaluate for adrenal sources of androgen excess 3.
Two-hour oral glucose tolerance test if diabetes or insulin resistance is suspected, as these conditions may be associated with hair loss and polycystic ovary syndrome (PCOS) 2.
Fasting lipid and lipoprotein levels to evaluate for dyslipidemia, which may be related to hair loss 2.
Specialized Testing for Specific Clinical Scenarios
Additional investigations are warranted only when the diagnosis is uncertain or presentation is atypical 2:
Fungal culture when tinea capitis (scalp ringworm) is suspected 2.
Serology for lupus erythematosus when systemic lupus is in the differential diagnosis 2.
Serology for syphilis when secondary syphilis is suspected 2.
Skin biopsy for difficult cases, early scarring alopecia, or diffuse alopecia areata that is challenging to diagnose 2.
Important Clinical Considerations
Most cases of alopecia areata are diagnosed clinically without laboratory workup, as investigations are unnecessary when the diagnosis is clinically evident 2. The British Journal of Dermatology emphasizes avoiding excessive laboratory testing in straightforward cases 2.
Common pitfalls to avoid:
- Ordering excessive laboratory tests when the diagnosis is clinically evident 2.
- Failing to consider the psychological impact of hair loss, which may warrant assessment for anxiety and depression 2.
- Overlooking dermoscopy as a non-invasive diagnostic tool that can provide valuable information, looking for yellow dots, exclamation mark hairs, and cadaverized hairs in alopecia areata 2.
Timing matters: Iron supplementation may result in better prognosis when started within 6 months of onset, as hair loss due to iron deficiency develops gradually over months 1.