HOT OCCUPATION AND NEPHROLITHIASIS

We investigated the prevalence of stone disease and urinary stone risk factors in machinists chronically exposed to a hot environment and ma ssive sweating, without interference of nephrotoxic metals or other li thogenic compounds. The study was performed at a glass plant and expos ure to heat stress was estimated by the Wet Bulb Globe Temperature cli matic index. The prevalence of nephrolithiasis on the entire populatio n of the machinists was 8.5% (20 of 236), while the prevalence on the controls working in normal temperature was 2.4% (4 of 165) (p = 0.03). A high incidence (38.8%) of uric acid stones was present in the worke rs exposed to heat stress. Among the urinary stone risk indexes determ ined for 3 days during the 8-hour work shift on a randomly selected sa mple of 21 workers exposed and 21 workers not exposed to heat stress w ithout any evidence of stone disease significant differences were foun d in uric acid concentration (722 +/- 195 versus 482 +/- 184 mg./l., p <0.001), specific gravity (1,026 +/- 4 versus 1,021 +/- 6, p <0.005) and pH (5.31 +/- 0.28 versus 5.64 +/- 0.54, p <0.02), respectively. Th us, high uric acid relative supersaturation was present during occupat ion in hot temperatures (8.67 +/- 3.49) compared to occupation in norm al temperatures (4.15 +/- 2.7) (p <0.001). This study confirms that ch ronic dehydration represents a real lithogenic risk factor, mainly for uric acid stones, and adequate fluid intake is recommended during hot occupations.