Serum β2-microglobulin at discharge predicts mortality and graft loss following kidney transplantation

Serum beta(2)-microglobulin (beta M-2), a novel marker of kidney function, predicts mortality and kidney failure in the general population, and its elevation following transplantation is a marker of acute rejection. The association between post-transplant serum beta M-2 and outcomes following kidney transplantation, however, is unknown. To help determine this, we conducted a retrospective cohort study of 2190 individuals receiving a primary kidney transplant with serum beta M-2 measured at discharge. A total of 452 deaths and 347 graft failures before death (669 total graft losses) occurred over a median of 4.1 years of follow-up. After adjustment, the highest quintile of beta 2M (5.0 mg/l and above), compared with the lowest quintile (<2.3 mg/l), was associated with a hazard ratio of 4.6 (95% confidence interval 2.8, 7.5) for death, 4.1 (2.4, 7.0) for death-censored graft loss, and 3.8 (2.5, 5.6) for total graft loss. Serum beta M-2 was more strongly associated with each outcome than was serum creatinine. Higher serum beta M-2 at discharge was independently associated with each outcome in models stratified by the presence of delayed graft function, donor type, or estimated glomerular filtration rate at discharge. Thus, serum beta M-2 at discharge is a potent predictor of long-term mortality and graft loss in kidney transplant recipients, providing information on allograft function beyond that of serum creatinine.