Urinary KIM-1, but not urinary cystatin C, should be corrected for urinary creatinine.
Clin Biochem 2016;
49:1164-1166. [PMID:
27475248 DOI:
10.1016/j.clinbiochem.2016.07.015]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 06/30/2016] [Accepted: 07/25/2016] [Indexed: 10/21/2022]
Abstract
OBJECTIVES
The interest for tubular damage markers such as urinary cystatin C (U-CystC) and kidney injury molecule-1 (U-KIM-1) grows, especially for the diagnosis of acute kidney injury. The trend to measure proteins in spot urine samples instead of 24-h urine collections calls for adjustment of urine dilution with urinary creatinine (UCr). However, it is not known whether UCr adjustment provides a more true value of basal U-CystC and U-KIM-1 levels than absolute values.
DESIGN & METHODS
This study examines the rationale for UCr correction for U-CystC and U-KIM-1 by exploring the linear relations between U-CystC and U-KIM-1 and UCr, respectively, and the biological day to day variation of absolute concentrations and UCr adjusted values of the two biomarkers.
RESULTS
Both U-CystC and U-KIM-1 concentrations correlated positively with UCr (R=0.37, P<0.001 and R=0.62, P<0.001, respectively) in 378 participants in a community cohort, which indicated a rationale for adjustment with UCr. However, U-CystC/Cr ratio associated negatively with UCr (R=- 0.31, P<0.001), which could indicate a certain amount of 'over-adjustment'. Morning urine collected for 10 consecutive days from 13 healthy volunteers showed a biological day to day variation of 82% for U-CystC, 75% for U-cystC/Cr ratio, 70% for U-KIM-1 and 46% for U-KIM-1/Cr ratio.
CONCLUSIONS
This study supports the use of U-KIM-1/Cr ratio in clinical population studies. Data supporting the use of U-CysC/U-Cr ratio were less convincing and the possible confounding of UCr has to be acknowledged in clinical settings.
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