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

ObjectivesGlobally, 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.DesignA cross-sectional study.SettingA shoe-making factory in West Java, Indonesia.Participants119 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 measuresArea 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.ResultsWBGT 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.ConclusionUrine specific gravity with a cut-off value of ≥1.018 could be used to detect nephrinuria among heat-exposed workers.

Impact of Heat Stress on Renal Function: A Systematic Literature Review Focusing on Workplace Heat

“…In 18 studies, wet bulb globe temperature (WBGT) index was calculated [12-14, 17, 18, 21, 22, 24, 25, 30-38]; 15 of these articles used the WBGT meter [12,14,17,18,21,22,25,[30][31][32][33][35][36][37][38]. In two of these studies, the index values were obtained from the safety engineering department [13,24], and in another study, the temperature and relative humidity were measured using a digital weather meter [34]. Furthermore, two studies measured the environmental temperature and did not calculate the heat indices [23,39].…”

“…Other Industries: In an investigation of 119 indoor heat-exposed individuals working at a shoemaking factory, decreased eGFR (i.e., <90mL/min/1.73m 2 ) was observed among 12.6% of the workers [13]. ACR: ACR was used by two eligible studies.…”

“…Other Industries: A study conducted in eight industrial sectors found that workers with a very high heat exposure combined with physical exertion had 3.6 times higher odds of increased USG (OR=3.6, P<0.001) [12]. Moreover, a study conducted on 119 indoor heat-exposed individuals working in a shoe-making factory showed that 64.7% of the workers had an abnormal USG level (i.e., USG of ≥1.020) [13]. In one study conducted among manufacturing workers, agricultural workers, police officers, tourism workers, and construction workers, no significant difference was reported in the mean of USG.…”

“…There is increasing evidence that HS is associated with a risk for kidney damage in populations at risk of CKDnt [10,12]. HS can lead to high body temperature and dehydration with subsequent volume depletion, which may cause kidney damage [12,13]. Heat-exposed workers such as miners and industrial and agricultural workers are prone to HS and subsequently develop CKDnt, because of manual work in hot environments, short breaks, and inadequate fluid intake [10,14].…”

“…The standard screening tests include the assessment of renal biomarkers such as serum creatinine and albuminuria. Further, urine-specific gravity is an inexpensive test that can accurately detect early kidney injury [13]. It is stated that CKDnt is prevalent mainly in young, male agricultural laborers [15].…”