Diagnostic performance and methodological concordance of the autologous sweat skin test for sweat allergy in a tropical setting: A pilot cross-sectional study

Abstract

BACKGROUND: Sweat allergy is frequently observed in patients with cholinergic urticaria (CholU) and atopic dermatitis (AD), yet data from high-sweating, tropical regions are scarce. The autologous sweat skin test (ASwST) is considered the reference diagnostic assay, but protocols differ. OBJECTIVE: To determine the prevalence of sweat allergy-assessed by the ASwST-in patients with CholU and AD in a tropical setting, and to evaluate concordance between the testing methods. METHODS: In this cross-sectional pilot study, 29 CholU patients, 41 AD patients, and 20 healthy controls underwent intradermal injection of filtered autologous sweat at 20 μL and 50 μL. Skin responses were assessed via wheal and flare formation. Positivity rate of sweat allergy using ASwST, clinical correlates, and inter-volume agreement were calculated. RESULTS: ASwST was positive in 8/29 CholU patients (27.6%) and 11/41 AD patients (26.8%); all controls were negative. In AD, positivity occurred across disease-severity strata. Overall inter-volume agreement reached 80%: 51/70 tests (72.9%) were negative for both volumes, and 5/70 (7.1%) were concordantly positive. The remaining 14/70 cases (20.0%) reacted only at 50 μL, yielding a significantly higher positivity rate than 20 μL (27.1% vs 7.1%, P = 0.001). CONCLUSIONS: In tropical Thailand, ASwST identified sweat allergy in approximately 25% of CholU and AD patients, lower than many temperate-zone reports. Either injection volume is acceptable; however, 50 μL increases diagnostic yield without compromising specificity. Larger, multicenter studies should clarify whether ambient heat, humidity, or cutaneous microbiota modulate sweat-allergy.