End-stage renal disease (ESRD) carries a high public health burden yet the influence of occupational risk factors is understudied. In a prospective study of autoworkers, we investigate the influence of exposure to metalworking fluids (MWF) on ESRD. We also examined the impact of mortality as a competing risk.
Methods Follow-up of 36,703 autoworkers was conducted for 1973 through 2009. Cumulative exposure to each type of fluid (straight, soluble, and synthetic) was estimated with a 15-year lag, with Cox proportional hazards regression to estimate Hazard Ratios (HR) and 95% confidence intervals (CI) for ESRD, both all cause and cause specific (hypertension and glomerulonephritis). Exposure was modelled using penalised splines and linear terms. We estimated the HR with mortality as a competing risk (CR) using both data augmentation and subdistribution hazard approaches. Models adjusted for age, time since hire, plant, year, gender, race, and other MWF types. Results were also examined separately for white males.
Results There were 551 ESRD cases (190 hypertension and 63 glomerulonephritis). Using a linear term for each MWF exposure, there was no association with any fluid type and ESRD overall, and these results did not change substantially when either type of CR model was used. However, penalised splines using standard regression provided more information about exposure-response curves for specific types of ESRD. For white males, soluble fluids were associated with hypertensive nephropathy and glomerulonephritis (at median 6.1 mg/m3-year: HR 1.03 95% CI: 1.03, 1.04, and HR 1.02 (1.02, 1.03), respectively) per mg/m3-year increase in exposure and straight fluids increased risk of glomerulonephritis (at median 0.9 mg/m3-year: HR 1.08 95% CI (0.78, 1.50), HR 1.02 95% CI (1.02, 1.03), respectively).
Conclusions Soluble and straight MWF were associated with ESRD. Accounting for mortality as a competing event did not substantially alter the relationship between MWF and ESRD.
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