Immune status monitoring of transplant recipients could identify patients at risk of acute rejection, infection, and cancer, which are important sources of morbidity and mortality in these patients. The ImmuKnow assay provides an objective assessment of the cellular immune function of immunosuppressed patients. Inconclusive results concerning the ability of the ImmuKnow test to predict acute rejection and infection have raised concerns about the predictive value of ImmuKnow in liver transplant recipients. We conducted a systematic literature review to identify studies published up to March 2012 that documented the use of ImmuKnow for monitoring immune function in liver transplant recipients. The study quality was assessed with the Quality Assessment of Diagnostic Accuracy Studies 2 score. We identified 5 studies analyzing ImmuKnow performance for infection and 5 studies analyzing ImmuKnow performance for acute rejection. The pooled sensitivity, specificity, positive likelihood ratio, diagnostic odds ratio, and area under the summary receiver operating characteristic curve were 83.8% [95% confidence interval (CI) ¼ 78.5%-88.3%], 75.3% (95% CI ¼ 70.9%-79.4%), 3.3 (95% CI ¼ 2.8-4.0), 14.6 (95% CI ¼ 9.6-22.3), and 0.824 6 0.034, respectively, for infection and 65.6% (95% CI ¼ 55.0%-75.1%), 80.4% (95% CI ¼ 76.4%-83.9%), 3.4 (95% CI ¼ 2.4-4.7), 8.8 (95% CI ¼ 3.1-24.8), and 0.835 6 0.060, respectively, for acute rejection. Heterogeneity was low for infection studies and high for acute rejection studies. In conclusion, the ImmuKnow test is a valid tool for determining the risk of further infection in adult liver transplant recipients. Significant heterogeneity across studies precludes the conclusion that ImmuKnow identifies liver transplant patients at risk for rejection. Liver Transpl 18:1245-1253, 2012. V C 2012 AASLD.Received April 18, 2012; accepted June 16, 2012.In the field of solid organ transplantation, the maintenance of an adequate level of immunosuppression is of the greatest importance. On the one hand, overimmunosuppression can promote the appearance of infection, cancer, and other undesirable secondary effects. Infectious diseases remain an important source of morbidity and mortality for all types of transplant patients. 1 Up to two-thirds of all liver Abbreviations: AUC, area under the curve; AUC-ROC, area under the receiver operating characteristic curve; CI, confidence interval; df, degrees of freedom; DOR, diagnostic odds ratio; HCV, hepatitis C virus; iATP, intracellular adenosine triphosphate; QUADAS-2, Quality Assessment of Diagnostic Accuracy Studies 2; SE, standard error; SROC, summary receiver operating characteristic.