Association between Occupational Cadmium Exposure and Markers of Kidney Injury: A Systematic Review and Meta-Analysis

Cadmium (Cd)-induced nephrotoxicity is a well-known phenomenon; however, several observational studies have used various biomarkers to monitor kidney injury in occupationally exposed populations. The markers used in these studies are found to be varied in sensitivity and are site-specific, and experts have the opinion that a single marker cannot predict the degree of kidney injury in human biomonitoring studies. Therefore, the current systematic review consolidates existing evidence to identify the association between Cd exposure and markers of potential sites of renal dysfunction/damage. Thirty (30) studies with 1980 chronic Cd exposure by occupations and 1292 unexposed were included in the review. The pooled mean difference of Cd exposure was as follows: blood Cd, 6.45 (5.18 to 7.71) μg/L; urine Cd, 4.52 (3.54 to 5.5) μg/g creatinine. Cd exposure was associated with impaired glomerular function (higher serum creatinine, serum β2 microglobulin, and lower creatinine clearance rate), tubular reabsorption (higher urinary β2 microglobulin and retinol binding protein), and injury (higher urinary <i>N</i>-acetyl-β-d-glucosaminidase and kidney injury molecule-1). However, the included studies exhibited high levels of heterogeneity. From the data, it is highly evident that biomarkers such as urinary <i>N</i>-acetyl-β-d-glucosaminidase, and retinol binding protein are found to be more sensitive than conventional clinical renal functional markers such as serum creatinine, urinary albumin, and protein levels, which are found to be within acceptable limits among the Cd-exposed group. Considering the rising disease burden of chronic kidney disease of unknown origin, Cd exposure-associated renal dysfunction and damage is a public health concern. Therefore, the review also discussed emerging biomarkers with higher sensitivity for early detection that can be adopted in occupational biomonitoring studies as early markers to prevent/delay the progression of kidney disease among the working population. Prospero Registration ID: CRD42022380923.