When maternal antibodies are no longer present, this applies to persons above the age of 12 months. CMV IgG levels in matched samples obtained one to three months apart can be utilized to diagnosis primary infection; seroconversion (first sample IgG negative, second sample IgG positive) is unambiguous evidence of recent primary infection. A fourfold rise in antibody titer between two consecutive tests indicates a previous infection has been resolved. CMV IgM testing may be useful in cases where the clinical presentation is atypical or if diagnostic uncertainty exists. It should not be used as the only means of diagnosing congenital infection because up to 20% of healthy infants have detectable IgM antibodies. The sensitivity of the test is limited by the timing of sampling after birth. CMV IgM antibodies appear early in the disease process and may remain detectable for up to a year after initial infection. A positive CMV IgG test result does not confirm a current infection. A negative test does not exclude active infection. A person with suspected active CMV infection should have additional testing performed to confirm or rule out active infection. Active CMV infection can cause significant morbidity and mortality among immunocompromised individuals such as those who receive chemotherapy for cancer or transplant recipients. Diagnosis of active infection requires detection of CMV in urine or saliva using sensitive methods such as polymerase chain reaction (PCR).