CMV is a significant cause of morbidity and mortality specially in organ transplant recipients and immunocompromised individuals. Positive CMV IgM results indicate recent CMV infection. These individuals may transmit CMV to susceptible individuals through blood and tissue products. It is also responsible for congenital disease of the newborn.Diagnosis of primary, acute phase infection with cytomegalovirus (CMV), especially in patients with infectious mononucleosis and pregnant women who, based on clinical signs or exposure, may have primary CMV infection. CMV is also responsible for congenital disease among newborns and is 1 of the TORCH infections (toxoplasmosis, other infections including syphilis, rubella, CMV, and herpes simplex virus). A negative cytomegalovirus (CMV) IgM results suggest that the patient is not experiencing a recent infection. However, a negative result does not rule out primary CMV infection. Positive CMV IgM results indicate a recent infection (primary, reactivation, or reinfection). IgM antibody responses in secondary (reactivation) CMV infections have been demonstrated in some CMV mononucleosis patients, in a few pregnant women, and in renal and cardiac transplant patients. Levels of antibody may be lower in transplant patients with secondary rather than primary infections.