Diagnostic role of urine specific gravity to detect kidney impairment on heat-exposed workers in a shoe factory in Indonesia: a cross-sectional study

Abstract

Objectives Globally, there are increasing cases of chronic kidney disease of unknown origin among heat-exposed workers. We aimed to see the kidney damages of indoor heat-exposed workers and whether urine specific gravity can predict any kidney damages.Design A cross-sectional study.Setting A shoe-making factory in West Java, Indonesia.Participants 119 subjects were included. Minimum total sample size was 62. Subjects were indoor heat-exposed workers who were exposed to occupational wet-bulb globe temperature (WBGT) of 28°C–30°C for 8 hours daily with 1 hour break, 5 days a week. The inclusion criterion was healthy subjects according to the result from annual medical check-up in 2019. The exclusion criteria were subjects who were taking vitamins and/or supplements that might cause disturbance in urine specific gravity and/or hydration status, pregnant and fasting.Primary and secondary outcome measures Area under the curve (AUC), sensitivity and specificity of urine specific gravity for the detection of urinary nephrin and urinary kidney injury molecule-1 (KIM-1) were analysed. Estimated glomerular filtration rate (eGFR) and quantitative albuminuria were also measured.Results WBGT in the work area of the subject was 28°C–30°C. There were 15 (12.6%) subjects who had eGFR <90 mL/min, but ≥60 mL/min. High serum vasopressin levels were found in 79 subjects with a mean of 6.54 (95% CI 5.94 to 7.14) ng/mL. Most subjects had nephrinuria (87.4%) with preserved renal function (87.4%). Several subjects had elevated urinary KIM-1 (10.9%) and albuminuria (7.6%). AUC of urine specific gravity for increased urinary nephrin was 81.7% (95% CI 68.8% to 94.6%) and statistically significant (p<0.001). Cut-off value of ≥1.018 for urine specific gravity has sensitivity of 71.2% and specificity of 80% for detecting elevation of urinary nephrin levels.Conclusion Urine specific gravity with a cut-off value of ≥1.018 could be used to detect nephrinuria among heat-exposed workers.