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

Serum β2-microglobulin (β2M), 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 β2M 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 β2M 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 β2M (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 β2M was more strongly associated with each outcome than was serum creatinine. Higher serum β2M 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 β2M 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.