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

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.

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.

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.

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.