β2-Microglobulin. A reliable parameter for differentiating between graft rejection and severe infection after cardiac transplantation

Abstract

We investigated the role of β2-microglobulin as a noninvastive parameter to monitor acute rejection and severe infection in 45 consecutive heart transplant recipients. Endomyocardial biopsy revealed moderate (41 patients) or severe (three patients) rejection in 44 patients. Severe infections of bacterial septicemia (11 patients), bronchopneumonia (two patients), and viral infection (seven patients) were detected by a meticulous schedule of various clinical and laboratory tests. β2-Microglobulin levels in serum, generally corrected for serum creatinine, were significantly elevated in patients with infections (median, 63 mg/l; range Q10-Q90, 3.47-10.27 mg/l) compared with levels in patients with rejection (p < 0.0001) or in patients in obviously good condition (p < 0.0001). At the onset of acute rejection, the median corrected β2-microglobulin serum level was 1.56 mg/l (range Q10-Q90, -0.05-3.46 mg/l) and was significantly different from the control group (p < 0.01). In addition, density function and empirical quantile analyses allowed us to define ranges of β2-microglobulin levels that would differentiate between rejection (2.05-3.46 mg/l) and infection (>3.46 mg/l). With these values, sensitivity and specificity were 0.9 and 0.938 for detection of infection and 0.23 and 0.925 for detection of rejection, respectively. By means of β2-microglobulin, two cases of infection were misinterpreted as rejection (10%), and four of 44 rejections were mistaken for infections (9%). We conclude that measurement of β2-microglobulin may improve the management of heart transplant patients.