Urinary excretion of -microglobulin as a prognostic marker in immunoglobulin A nephropathy

Background/Aims: ${\beta}_2$-microglobulin (${\beta}_2$-MG) is freely filtered at the glomerulus and subsequently reabsorbed and catabolized by proximal renal tubular cells. Urinary ${\beta}_2$-MG is an early and sensitive biomarker of acute kidney injury; however, its utility as a biomarker of immunoglobulin A nephropathy (IgAN) is unclear. Methods: We included urinary ${\beta}_2$-MG levels in the routine laboratory examination of all inpatients with biopsy-proven IgAN at our hospital from 2006 to 2010. We retrospectively analyzed the correlation between ${\beta}_2$-MG levels and clinical parameters as a prognostic biomarker of IgAN. Results: A total of 51 patients (30 males, 21 females; mean age, $33.01{\pm}12.73$ years) with IgAN were included in this study. Initial demographic, clinical, and laboratory data for all patients are listed. The mean initial estimated glomerular filtration rate and 24-hour urine protein levels were $94.69{\pm}34.78mL/min/1.73m^2$ and $1.28{\pm}1.75g/day$, respectively. The mean level of urinary ${\beta}_2$-MG was $1.92{\pm}7.38{\mu}g/mg$ creatinine. There was a significant correlation between initial serum creatinine (iSCr), urine protein creatinine ratio (UPCR), and the level of ${\beta}_2$-MG (r = 0.744, r = 0.667, p < 0.01). There was also a significant correlation between renal function tests and the level of urinary ${\beta}_2$-MG (p < 0.01). Cox regression analysis showed that albumin, ${\beta}_2$-MG, iSCr, and UPCR were significant predictors of disease progression in IgAN. Conclusions: Urinary ${\beta}_2$-MG levels showed a significant correlation with renal function and proteinuria in IgAN. Thus, we propose that urinary ${\beta}_2$-MG may be an additional prognostic factor in patients with IgAN.