Introduction Epidemic chronic kidney disease of unknown cause (CKDu) occurs among sugar cane workers, notably cane cutters doing heavy manual work in hot tropical environments in Mesoamerica. Repetitive dehydration consequent on strenuous work in heat is posited as the cause. A Nicaraguan cohort study showed remarkable kidney function decreases across six weeks of the cane cutting season consistent with the dehydration hypothesis. This Nicaraguan study was replicated on a sugar plantation in South Africa about 3 500 kms from the equator and cooler than previous study locations to examine whether less extreme ambient conditions resulted in reduced kidney stress.

Methods 38 cane cutters and 36 referents of similar socio-economic status but doing less strenuous work on the same plantations provided pre- and post-shift blood and urine samples for measures of kidney function and hydration on Day 1 and Week 9 of the cutting season. Frozen specimens were transported to a chemical pathology laboratory in Johannesburg for analysis. Parameters measured included cystatin C, eGFR (derived from cystatin C), serum creatinine, serum neutrophil gelatinase-associated lipocalin (NGAL), serum uric acid and osmolality.

Results Minimum and maximum temperatures were 20.9 and 26.5o C on Day 1 and 13.6 and 26.6 o C on Week 9. There were clinically modest, albeit statistically significant, increases in mean cystatin C pre-shift values between Day 1 and Week 9 in the cane cutters: 0.847 to 1.011 mg/L (p=0.00) which means a considerable decline in eGFR. Other results were not consistent among the various markers of effect on the kidneys. The magnitude of the increase in cystatin C among referents was similar to the cutters: 0.771 to 0.904 mg/L.

Conclusions Kidney function markers seemed to be much less affected in the cooler study location than in the hotter one.