antigenemia

Antigenemia is the presence of circulating antigens in the bloodstream, typically arising from infection or tissue injury. It is detected by antigen-detection assays and is conceptually related to, but distinct from, viremia, which refers to whole pathogens in the blood.

In infectious disease, antigens released from pathogens or infected host cells can enter the bloodstream. In immunocompromised patients, antigenemia can reflect active replication or tissue invasion even when direct detection of the pathogen is difficult.

A prominent example is the CMV pp65 antigenemia assay, used to monitor cytomegalovirus infection in transplant recipients and other immunosuppressed patients. The test detects CMV pp65 protein within peripheral blood leukocytes and is reported as the number of positive cells per a fixed leukocyte count. Antigenemia testing may complement or precede nucleic acid testing, such as PCR, in some settings.

Limitations of antigenemia include reduced sensitivity in patients with low white blood cell counts and the need for specialized laboratory methods. In many centers, nucleic acid testing has largely supplanted antigenemia due to higher sensitivity and broader applicability.

In broader terms, antigenemia describes circulating pathogen-derived or host-derived antigens in the blood and is used in various diagnostic contexts. The specific assays and interpretations vary by pathogen and clinical setting.