Stability of alpha1-microglobulin, beta2-microglobulin and retinol binding protein in urine

The stability of alpha1-microglobulin (α1M), beta2-microglobulin (β2M) and retinol binding protein (RBP) in urine was determined in 135 random samples from children with renal disease, febrile illness, malignancy, and from controls. Immediately after voiding, samples were divided into two portions, one of which was alkalinised. After identical transit times and laboratory handling the pH and concentrations of the individual proteins in each pair were measured. β2M was unstable in urine of pH < 7 and grossly so below pH 6. In some instances β2M was low or undetectable even in the alkalinised samples when α1M and RBP levels were raised, suggesting that degradation of β2M may have occurred prior to voiding. Concentrations of α1M and RBP were significantly lower in the non-alkalinised fractions at pH < 7, although to lesser degree than for β2M. Contrary to previous reports, we conclude that the stability of all 3 proteins is affected by urinary pH and recommend that this be measured and alkalinisation performed at the time of voiding.