Cytomegalovirus load in whole blood is more reliable for predicting and assessing CMV disease than pp65 antigenaemia.

CMV is a common cause of disease in immunocompromised patients. Because sampling of the diseased organ can be invasive, markers of systemic CMV reactivation such as pp65 and CMV viral load are commonly used to monitor patients at risk of CMV disease. In this retrospective analysis, the performance of these markers was compared in solid organ transplant recipients, patients with haematological malignancies and HIV infection. Both assays were sensitive markers of reactivation, however, the predictive value for disease of a positive result for both was low. Compared to viral load, the pp65 assay was a less sensitive marker of CMV reactivation. It was only positive when the viral load was greater than 3 log (10) copies/ml whole blood and was negative in 10 instances when the viral load was between 3 and 5 logs. In concordantly positive samples, the number of pp65 positive cells varied widely relative to the viral load and the number of positive cells counted could not be used to predict disease likelihood with any certainty. To conclude, CMV viral load provides a more consistent guide to determine likelihood of disease than pp65 count and is a more sensitive marker of CMV reactivation.