[[Alpha].Sub.1]-Microglobulin Is Stable in Human Urine Ex Vivo (Letters) (Letter to the Editor‪)‬

To the Editor: Increased concentrations of urinary [[alpha].sub.1]-microglobulin may imply proximal tubular damage (1). [[alpha].sub.1]-Microglobulin has generally been considered to be stable in human urine (1, 2). Tencer et al. (2) observed good stability in 10 urine samples stored at room temperature for 7 days, at 4 [degrees]C for 30 days, and at -20 [degrees]C for 6 months. In contrast, Donaldson et al. (3) noted significant losses of [[alpha].sub.1]-microglobulin in urine stored at -20 [degrees]C and that this problem was exacerbated in more acidic (pH 6.0) urines; they recommend that urine should be neutralized on receipt. The manufacturers of our assay recommend that urines be assayed fresh or stored at 4 [degrees]C for a period of less than 1 week and warn against freezing samples. Urine samples are often stored before batch analysis. To clarify the appropriate storage conditions for urinary [[alpha].sub.1]-microglobulin, we studied stability under standardized conditions.