Alopecia, hair loss

Laboratory tests

• No routine tests for hair loss: the prescription depends on the clinical form (see the following tabs).

Laboratory tests

• Serum ferritin (if clinical suggestion or deficiency factor)if needednon-French guidelineLooking for iron deficiency, one of the discussed triggers; threshold and value of supplementation remain debated ^[9,10]. The American Family Physician review measures it on clinical grounds ^[2].
• TSH (if clinical suggestion)if needednon-French guidelineThyroid dysfunction is among the triggers: an Indian consensus puts TSH in its baseline tests ^[9], and the Androgen Excess and PCOS Society calls it optional but recommended in female alopecia ^[11]. The American Family Physician review measures it on clinical grounds ^[2].
• FBCif needednon-French guidelinePlaced by an Indian expert consensus in the baseline tests of any diffuse hair loss ^[9]; weak evidence.
• Syphilis serology (if irregular "moth-eaten" patches or risk factor for STI)if neededMultiple, irregular, “moth-eaten” patches of alopecia (clearings), or diffuse thinning, in an exposed patient or with other signs of secondary syphilis: syphilitic alopecia affects 2.9 to 7% of secondary syphilis and is confused with alopecia areata, tinea capitis or telogen effluvium ^[3].

Laboratory tests

• Total testosterone (if looking for hyperandrogenism)if needednon-French guidelineThe Androgen Excess and PCOS Society (2019) considers it mandatory to look for androgen excess in every affected woman ^[11]. The international PCOS guideline (2023) points out that isolated alopecia, without hirsutism, is a poor predictor of biochemical hyperandrogenism ^[12]. The American Family Physician review does not propose hormonal tests in women ^[2].
• SHBG (if testosterone is measured, to calculate the free androgen index)if needednon-French guidelineWith testosterone, to calculate the free androgen index ^[12]. Same positions as for testosterone ^[2,11,12].
• Serum prolactin (if looking for hyperandrogenism)if needednon-French guidelineCalled optional but recommended by the Androgen Excess and PCOS Society, of uncertain value: 7.2% raised prolactin and 1.8% prolactinoma in a series of 109 women ^[11].
• TSH (if clinical suggestion)if needednon-French guidelineCalled optional but recommended by the Androgen Excess and PCOS Society ^[11]. The American Family Physician review does not propose hormonal tests in women ^[2].
• Serum ferritin (if clinical suggestion or deficiency factor)if needednon-French guidelineIron is called optional but recommended by the Androgen Excess and PCOS Society ^[11]. The American Family Physician review measures it on clinical grounds ^[2].
• Delta-4-androstenedione (if testosterone normal)if needednon-French guidelineNormal total and free testosterone while hyperandrogenism is still suspected: androstenedione may be measured, less specific ^[12].
• DHEA-S (if testosterone normal)if needednon-French guidelineNormal total and free testosterone: DHEA-S may be measured, less specific and falls with age ^[12].
• 17-hydroxyprogesterone (if androgens very high)if needednon-French guidelineAndrogens well above normal: look for a cause other than PCOS, including congenital adrenal hyperplasia, an ovarian or adrenal tumour, Cushing's syndrome ^[12].
• On the combined oestrogen-progestogen pill, androgens cannot be interpreted: if the assay is essential, stop the pill for at least 3 months (other contraception in the meantime).

Laboratory tests

• Typical form (gradual onset, family history, temporal recession, vertex, normal scalp): no tests, including before finasteride or minoxidil.
• Sudden, diffuse or patchy hair loss, abnormal scalp or general signs: this is not typical androgenetic alopecia; see the tabs "Diffuse hair loss (telogen effluvium)", "Alopecia areata" or "Scarring or inflammatory alopecia".

Laboratory tests

• No tests are needed in most cases of alopecia areata.
• TSH (adult with alopecia totalis or universalis, or child at risk)if needednon-French guidelineAdults: screening is debated, to be considered mainly in total or universal alopecia areata; children: only if trisomy 21 (Down syndrome), atopy, family history of thyroid disease or clinical signs ^[6].
• Anti-TPO antibodies (with the TSH, same indications)if needednon-French guidelineIf thyroid screening is done, the British recommendation pairs TSH with thyroid autoantibodies ^[6].
• Syphilis serology (if diagnostic doubt)if neededDiagnostic doubt: secondary syphilis can mimic alopecia areata ^[3,6].

Mycological examination (as soon as possible, without delaying treatment)

• Mycological sample from the scalp: broken hairs and scales, pus on a swab if kerion (direct examination and culture)
• Preferably before any antifungal. If an antifungal has already been applied, some laboratories ask for a break of 15 days (topical treatment) or 3 months (oral treatment): check with the laboratory, without delaying empirical treatment.
• ASTif neededRisk factor for liver damage: routine liver monitoring is not established in children, it is decided case by case ^[15,16].
• ALTif neededRisk factor for liver damage: routine liver monitoring is not established in children, it is decided case by case ^[15,16].
• GGTif neededRisk factor for liver damage: routine liver monitoring is not established in children, it is decided case by case ^[15,16].

Contacts

• Siblings and parents: scalp examination and mycological sample, as early as possible (prescription in each person's name). Pet: veterinarian, even if it looks healthy.

Specialist opinion

• Refer to a dermatologist, who decides on a scalp biopsy: follicular openings lost (scarring alopecia) or inflamed scalp without an obvious diagnosis.

Laboratory tests (only if the context requires)

• Syphilis serology ("moth-eaten" patches or risk factor for STI)if neededIrregular “moth-eaten” patches or diffuse thinning in an exposed patient: syphilitic alopecia, non-scarring, mimics alopecia areata, tinea capitis or effluvium ^[3]; secondary syphilis is among the differential diagnoses of tinea capitis ^[17].
• TSH (if lichen planopilaris or frontal fibrosing alopecia diagnosed)if needednon-French guidelineLichen planopilaris or frontal fibrosing alopecia confirmed by the dermatologist: hypothyroidism in 17 to 19% of patients in a meta-analysis of observational studies, whose authors propose thyroid tests in all ^[22]. Authors' proposal, not a recommendation.
• Discoid lupus, or signs of involvement of other organs: see the page "Systemic lupus: initial tests and laboratory monitoring in the community".