Effect of up to 30-days of storage at different temperatures on detection of feline kidney injury molecule-1 in urine

Background In humans, kidney injury molecule-1 (KIM-1) is a biomarker of acute kidney injury that can be quantified in urine. Preliminary investigation in cats with experimentally induced acute kidney injury showed that KIM-1 urine concentration correlated with kidney injury histopathology scores. A lateral flow assay (LFA) has recently become available for patient-side feline KIM-1 measurement. In vitro parameters of the assay have not yet been determined. The objectives of this study were to determine detection of KIM-1 in urine stored at different temperatures over time, to establish the linear range of the LFA, and to assess the intra-assay repeatability of measurements. Results Ten urine samples with a range of KIM-1 concentrations were stored at room temperature (22 o C), 4 o C or -20 o C, and tested with the LFA on days 0, 1, 2, 3, 7, 14, and 30. The concentration of KIM-1 in samples was not significantly different from the day 0 value, except one sample that had been stored for 30 days at room temperature yielded a significantly higher value. The assay results had a correlation coefficient of 0.922. The mean coefficient of variation for all samples was 15.7%. The slope of the curve of expected versus measured values in samples diluted two-fold nine times was 0.908, and results were linear over all dilutions. Conclusions The LFA for feline KIM-1 yields consistent results from stored urine samples. These characteristics will allow for KIM-1 to be measured retrospectively if immediate testing is not feasible. Within assay precision was high, and linearity over 9 logs of dilution suggests suitability for a range of subclinical and clinical kidney injuries.