Determination of the number of blood samples needed for optimal detection of cytomegalovirus viremia in immunocompromised patients using a shell-vial assay.

To establish the number of blood samples necessary for the diagnosis of viremic episodes caused by cytomegalovirus (CMV), a prospective analysis was conducted of 238 patients (38 renal transplant recipients and 200 HIV-infected patients) who developed CMV viremia. The usefulness of samples and the volume of blood required to demonstrate the presence of viremia by CMV was also studied. The first blood sample was diagnostic for CMV viremia in 53.3% of the viremic patients; the second sample documented an additional 22.2% of cases of viremia (75.5% of infected patients); and the third sample demonstrated viremia in the remaining 24.5%. Thus, a diagnosis of CMV viremia was established in every patient (100% of episodes of viremia). In this study, the use of three 3 ml blood samples collected at 24 h intervals was sufficient to detect all episodes of CMV viremia in patients clinically suspected to have disseminated disease.