Effect of pH on the stability of kidney injury molecule 1 (KIM-1) and on the accuracy of its measurement in human urine.
BACKGROUND
Urinary KIM-1 is a novel biomarker for tubular kidney damage, however little is known about its stability. The goal of this study is to examine the effect of urinary pH on the stability of KIM-1.


METHODS
Urine samples were collected from 45 volunteers. Samples were aliquoted, adapted to different pH values (range 4 to 9) and stored at -80°C. After thawing, each aliquot was divided into two, of which one was used to measure KIM-1 (human tim-1/kim-1/Havcr Elisa kit; R&D systems) at the same pH at which it was stored, while the other was readapted to pH 7 before measurement.


RESULTS
KIM-1 values of aliquots of the same sample are stable when stored at pH 6, 7 and 8 whereas at lower and higher storage pH, KIM-1 levels decrease significantly. When samples are readjusted to a neutral pH just before KIM-1 measurement, there are no longer significant differences between KIM-1 in aliquots stored at different pH values.


CONCLUSIONS
No effect of urinary pH on the stability of KIM-1 was seen. However, the only commercially available human tim-1/kim-1/Havcr Elisa kit of RD systems is pH dependent and we therefore suggest samples should be adjusted to neutral pH before measurement.
Pennemans
Valérie
V
Biomedical Research Institute, Hasselt University and transnational University Limburg, School of Life Sciences Diepenbeek, Belgium. valerie.pennemans@uhasselt.be
De Winter
Liesbeth M
LM
Faes
Christel
C
Van Kerkhove
Emmy
E
Reynders
Carmen
C
Rigo
Jean-Michel
JM
Swennen
Quirine
Q
Penders
Joris
J
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D000072596:Hepatitis A Virus Cellular Receptor 1; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000652:urine*; D008875:Middle Aged; D055550:Protein Stability; D011991:Receptors, Virus / Q000737:chemistry*; D013048:Specimen Handling; D016482:Urinalysis / Q000379:methods*; D055815:Young Adult
C491143:HAVCR1 protein, human; D000072596:Hepatitis A Virus Cellular Receptor 1; D008562:Membrane Glycoproteins; D011991:Receptors, Virus