(mark'ĕr )

1. A device or substance used to indicate or mark something.
2. An identifying characteristic or trait that allows apparently similar materials or disease conditions to be differentiated.

biochemical m.Any biochemical compound such as an antigen, antibody, abnormal enzyme, or hormone that is sufficiently altered in a disease to serve as an aid in diagnosing or in predicting susceptibility to the disease.

fecal m.A substance, such as carmine, ingested to mark the beginning and end of fecal collection periods.

genetic m.An identifiable physical location on a chromosome, e.g., a gene or segment of DNA with no known coding function, whose inheritance can be monitored.

process m.A measurable component of the health care given to patients with a specific disease or condition, used as an indicator of the overall quality of care given to patients with other conditions.

prognostic m.Any finding or characteristic that indicates that a disease is likely to improve, remit, or relapse.

risk m.Risk factor.

skin m.Ink or stain used to highlight, identify, or outline surgical sites. Also known as: surgical skin marker.

surrogate m.An indirect indicator of a disease state or of its response to therapy. Such markers often include laboratory tests thought to represent clinical progress accurately. For example, in diabetes mellitus, the glycosylated hemoglobin level is used as a marker of glycemic control; in AIDS the level of HIV RNA is used as a marker of disease progression.

tumor m.A substance whose presence in blood serves as a biochemical indicator for the possible presence of a malignancy. Examples of markers and the malignancies they may indicate are carcinoembryonic antigen for cancers of the colon, lung, breast, and ovary; beta subunit of chorionic gonadotropin for trophoblastic and testicular tumors; alpha-fetoprotein for testicular teratocarcinoma and primary hepatocellular carcinoma; and prostate-specific antigen for prostate cancer.