Using the newer Kidney Disease: Improving Global Outcomes criteria, beta-2-microglobulin levels associate with severity of acute kidney injury

Beta-2-microglobulin (B2M) is a marker of proximal tubular injury and glomerular filtration. Analyses using older/non-standardized definitions have shown low efficacy of B2M to predict acute kidney injury (AKI). We assessed if elevated levels of B2M would associate with either the diagnosis of AKI [under current Kidney Disease: Improving Global Outcomes (KDIGO) criteria] or recovery from AKI. We performed a retrospective study, including children who had urine B2M (uB2M) and/or serum B2M (sB2M) measured by immunoturbidimetry in our clinical laboratory between January 2011 and December 2015. We defined AKI based on KDIGO criteria [increase of serum creatinine (sCr) 0.3 mg/dL over 48h or >50% baseline over 7 days] or urine output <0.5 mL/kg/h for 24 h. Recovery from AKI was defined as a return to baseline sCr within 6 months. We calculated receiver operating characteristics (ROC) area under the curve (AUC). Of 529 patients, 245 developed AKI. Serum and uB2M associated with AKI development (AUCs 0.84 and 0.73, respectively). Patients had a graded higher median sB2M and uB2M with each higher AKI stage. sB2M differentiated Stage I from Stage III AKI (P < 0.001) and Stage II from Stage III AKI (P = 0.004). However, neither uB2M nor sB2M levels associated with recovery from AKI. Only older age {hazard ratio [HR] 0.97, [95% confidence interval (CI) 0.94-0.99]} and need for dialysis [HR 0.39 (95% CI 0.23-0.61)] predicted incomplete recovery after AKI. Using KDIGO criteria, sB2M and uB2M associate with the severity of AKI. Given its relative ease and lower cost, we suggest more widespread use of B2M for AKI detection.