Introduction There is an epidemic of Chronic Kidney Disease of undetermined cause (CKDu) in Central America causing the death of tens of thousands of agricultural workers. We have undertaken a community-based cohort study to identify factors associated with loss of kidney function in young adults at high risk of CKDu. The aim of this analysis was to characterise the associations between urinary findings at baseline and loss of kidney function (eGFR) over the follow-up period.

Methods We analysed urine samples from 350 apparently healthy men and women (ratio 3:1) from 9 communities in northwest Nicaragua. Semi-quantitative analysis using urine test strips (Siemens Multistix10 SG Reagent Strips) was performed on stored frozen samples. Albumin and creatinine levels were quantified using bromocresol green and Jaffe methods, respectively. Metals were analysed by ICP-Mass Spectrometry. Test strip findings were compared between the group with more stable function and the group with declining eGFR. Linear regression was used to investigate the associations between urinary metal concentrations and change in eGFR.

Results The majority of study participants had normal test strip results however there was an association between increased proteinuria (but without evidence of elevated albumin) in the declining group in comparison to the stable group (p=0.03). Aluminium and cadmium levels were above accepted limits compared to the general population, but no association with loss of eGFR was found.

Discussion A urine strip test is unlikely to be useful in identifying those with early CKDu. The positive urine strip test for protein in the absence of albuminuria in a proportion of those with declining kidney function likely indicates the presence of other proteins of tubular origin. Our data suggest high levels of overall exposure to aluminium and cadmium but do not suggest these metals have a causal role in loss of kidney function.