Table 2A.

Stability of urinary biomarkersa

Collection and ProcessingMean Percentage Difference (95% confidence interval of mean % difference) when Compared to Immediate Storage at −80°C
KIM-1, n = 6NAG, n = 6NGAL, n = 6
Remain at RMb for 2 h, then storage at −80°C−0.26 (−5.52 to 5.01)0.05 (−3.09 to 3.20)−2.45 (−6.54 to 1.64)
Remain at RM for 4 h, then storage at −80°C1.43 (−5.39 to 8.25)0.48 (−3.19 to 4.15)−5.3 (−14.89 to 4.30)
Remain at RM for 6 h, then storage at −80°C−3.97 (−10.80 to 2.86)0.48 (−2.42 to 3.38)2.54 (−7.86 to 12.93)
Remain at RM for 24 h, then storage at −80°C−6.52 (−11.73 to −1.30)−0.43 (−1.46 to 0.60)−9.78 (−22.55 to 3.00)
Remain at 4°C for 2 h, then storage at −80°C1.25 (−4.98 to 7.48)0.04 (−4.10 to 4.17)−3.97 (−9.91 to 3.77)
Remain at 4°C for 4 h, then storage at −80°C0.43 (−5.37 to 6.23)2.38 (−1.75 to 6.51)6.65 (0.46 to 12.84)
Remain at 4°C for 6 h, then storage at −80°C0.16 (−5.61 to 5.92)2.07 (−0.69 to 4.83)−5.19 (−13.47 to 3.09)
Remain at 4°C for 24 h, then storage at −80°C−2.33 (−7.94 to 3.27)2.26 (−1.90 to 6.42)−1.01 (−14.52 to 12.5)
Protease inhibitor versus no protease inhibitor1.23 (−3.76 to 6.23)−0.21 (−4.53 to 4.11)−1.51 (−7.23 to 4.20)
Prolonged storage at −80°C
    1 yr with 3 repeat freeze and thaw cycles−0.53 (−8.57 to 7.50)4.96 (1.51 to 8.41)−2.43 (−13.53 to 8.66)
    2 yr with 3 repeat freeze and thaw cyclesNA2.13 (−4.47 to 8.72)NA
  • a Immediate storage at −80°C and place urine samples at −80°C within first 20 min after initial collection.

  • b RM, room temperature; NA, not applicable.