Collection and storage requirements for urinary kidney injury molecule-1 (KIM-1) measurements in humans.

Background: Urinary kidney injury molecule-1 (KIM-1) is a recently discovered biomarker for early renal damage. However, little is known about the collection and storage requirements prior to its measurement in human urine.
Methods: Samples of healthy volunteers were collected and aliquoted. The effect of pre-freezing time, thawing, addition of protease inhibitors, centrifugation, storage time (up to 1.5 years) and temperature (4°C, -20°C and -80°C) was tested.
Results: Addition of protease inhibitors and centrifugation prior to freezing did not affect the KIM-1 measurements. When samples were kept at room temperature for longer than 3 h before freezing or defrosted more than 1 h before measurement, mean KIM-1 values differed significantly compared to aliquots with minimal pre-freezing and thawing time. Samples frozen at -80°C were stable for up to 1.5 years; however an increasing number of freeze-thaw cycles adversely affected KIM-1 measurements. When stored at 4°C and -20°C, samples were less stable compared to those stored at -80°C.
Conclusions: This study recommends that urine samples collected for KIM-1 measurements are frozen within 3 h after voiding and only be defrosted immediately prior to measurement. Addition of protease inhibitor and centrifugation prior to measurement is not necessary. Samples are preferably stored at -80°C and freeze-thaw cycles should be avoided.