Baseline urinary KIM-1 concentration in detecting acute kidney injury should be interpreted with patient pre-existing nephropathy

OBJECTIVES: To determine whether pre-existing nephropathy impacts urinary KIM-1 levels, urinary KIM-1 were measured in patients with normal kidney filtration function but either with or without proteinuria. The reference intervals of urinary KIM-1 in adults with normal kidney filtration function but without urine proteinuria were established. DESIGN AND METHODS: 188 urine samples were obtained from adults with normal kidney filtration. 83 of the 188 showed negative urine protein, erythrocytes and leucocytes were used as normal controls. The remaining 105 samples showed at least one abnormal result suggesting possible pre-existing nephropathy. Urinary KIM-1 concentrations were measured using an enzyme-linked immunosorbent assay. Urinary KIM-1 was normalized with urine creatinine concentration. The reference interval for urinary KIM-1 was determined by non-parametric methodology on 147 individuals. RESULTS: The results showed significantly increased urinary KIM-1 concentration in protein positive (protein +, erythrocyte +/−, leucocyte+/-) samples compared to controls (protein-, erythrocyte -, leucocyte -). Urinary KIM-1 concentrations were significantly higher when proteinuria was at trace concentration (0.25 g/L) and correlated with the severity of proteinuria. The creatinine normalized urinary KIM-1 was significantly higher when urine protein was 1 + to 3+ (0.75–5 g/L). The reference interval for urinary KIM-1 was 0.00 (90%CI: 0-0) to 4.19 (90%CI: 3.11–5.62) μg/L, and for creatinine normalized urinary KIM-1 0.00 (90%CI: 0-0) to 0.58 (90%CI: 0.44–0.74) μg/mmol. CONCLUSIONS: Baseline urinary KIM-1 concentrations were increased when there was detectable urine protein and correlated with its severity. The urinary KIM-1 concentrations should be interpreted with consideration of urine protein levels in individual patients.