Supplementary Material for: Electrochemical Skin Conductance in Diabetic Kidney Disease

Background: There is a need to identify patients with diabetic kidney disease (DKD) using noninvasive, cost-effective screening tests. Sudoscan®, a device using electrochemical skin conductance (ESC) to measure sweat gland dysfunction, is valuable for detecting peripheral neuropathy. ESC was tested for association with DKD (estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m²) in 383 type 2 diabetes mellitus (T2D)-affected patients; diagnostic thresholds were determined in 540 patients. Methods: Relationships between ESC with eGFR and urine albumin:creatinine ratio (UACR) were assessed in 202 European Americans and 181 African Americans with T2D. Results: In 92 European American DKD cases and 110 T2D non-nephropathy controls, respectively, mean (SD) ages were 69 (9.7) and 61 (10.8) years, hemoglobin A1c (HbA1c) 7.4 (1.2) and 7.4 (1.3)%, eGFR 29.6 (12.2) and 87.8 (14.2) ml/min/1.73 m², and UACR 1,214 (1,705) and 7.5 (5.8) mg/g. In 57 African American cases and 124 controls, respectively, mean (SD) ages were 64.0 (11.9) and 59.5 (9.7) years, HbA1c 7.4 (1.3) and 7.5 (1.7)%, eGFR 29.6 (13.3) and 90.2 (16.2) ml/min/1.73 m², and UACR 1,172 (1,564) and 7.8 (7.1) mg/g. Mean (SD) ESC (μS) was lower in cases than controls (European Americans: case/control hands 49.5 (18.5)/62.3 (16.2); feet 62.1 (17.9)/73.6 (13.8), both p < 1.3 × 10^-6; African Americans: case/control hands 39.8 (19.0)/48.5 (17.1); feet 53.2 (21.3)/63.5 (19.4), both p ≤ 0.01). Adjusting for age, sex, body mass index and HbA1c, hands and feet ESC associated with eGFR <60 ml/min/1.73 m² (p ≤ 7.2 × 10^-3), UACR >30 mg/g (p ≤ 7.0 × 10^-3), UACR >300 mg/g (p ≤ 8.1 × 10^-3), and continuous traits eGFR and UACR (both p ≤ 5.0 × 10^-9). HbA1c values were not useful for risk stratification. Conclusions: ESC measured using Sudoscan® is strongly associated with DKD in African Americans and European Americans. ESC is a useful screening test to identify DKD in patients with T2D.