Stability of Bence Jones protein in refrigerated urine samples over five days: a preanalytical evaluation

This study investigates the short-term stability of Bence Jones protein (BJP) in refrigerated urine samples stored over a period of 5 days. The aim was to evaluate whether BJP concentrations remain consistent when urine specimens are refrigerated and analyzed over time.

Urine samples were collected from 20 plasma cell dyscrasia patients with BJP for a total of 30 independent time-series and 83 data-points. Measurements were performed at five time points: Day 0 (baseline), and Days 1 through 4. Percentage difference (PD%) from baseline was used to quantify temporal change.

The median baseline BJP M-spike percentage was 54 % (range: 17-87 %), covering a wide range of total urinary protein (median 296 mg/L, range 64-3,094 mg/L). PD% ranged from -2 % on Day 3 to +7 % on Day 1, with no statistically significant trend over time. The derived instability equation, PD%=0.33 × time (days), yielded r= -0.03 and p=0.77, indicated negligible instability.

These findings demonstrate acceptable short-term stability of BJP in refrigerated urine over 5 days, supporting its use in routine laboratory workflows involving delayed analysis.