Nephrotoxicity-induced proteinuriaincreases biomarker diagnostic thresholdsin acute kidney injury

Fahim Mohamed1,2,3,4,8*, Nicholas A. Buckley1,4, John W. Pickering5,6, Klintean Wunnapuk7, Sandamali Dissanayake1,Umesh Chathuranga1, Indika Gawarammana1, Shaluka Jayamanneand Zoltan H. Endre3,5 

Background: Paraquat ingestion is frequently fatal. While biomarkers of kidney damage increase during paraquatinduceacute kidney injury (AKI), significant concurrent proteinuria may alter diagnostic thresholds for diagnosis and prognosis to an unknown extent. This study evaluated the effect of albuminuria on biomarker cutoffs for diagnosis and outcomprediction.

Methods: This was a multi-centre prospective clinical study of patients following acute paraquat selfpoisoning in 5 Sri Lankan hospitals. Biomarker concentrations were quantified using ELISA and microbead assays and correlated with urinaralbumin. Functional-AKI was defined by the Acute Kidney Injury Network serum creatinine definition and alternatively ba 50% increase in serum cystatin C. Albuminuria was defined as albumin-creatinine ratio >30 mg/g. The study outcomewere compared with a retrospective analysis of a preclinical study of paraquatinduced nephrotoxicity with appropriatcontrols.

Results: Albuminuria was detected in 34 of 50 patients, and increased with functional-AKI severity. The concentrations of uNGAL, uCysC, uClusterin, uβ2M, and uKIM-1 were higher in albuminuric compared to non-albuminuric patients (< 0.001). Albuminuria correlated with biomarker concentration (r > 0.6, p < 0.01) and was associated with death (p = 0. 006). Optimal biomarker cutoffs for prediction of death were higher in the albuminuric group. Similar outcomes with more detailed analysis were obtained in experimental paraquat nephrotoxicity.

Conclusion: Albuminuria was associated with paraquatinduced nephrotoxicity and increased excretion of low-moleculaweight protein biomarkers. AKI biomarker cutoffs for diagnosis, outcome prediction and AKI stratification increased in the presence of albuminuria. This may lead to over-diagnosis of AKI in conditions independently associated with proteinuria.

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