Biomarker (or biological marker)

an objectively measured variable or trait that is used as an indicator of a normal biological process, a disease state, or effect of a treatment. It may be a physiological measurement (height, weight, blood pressure, etc.), blood component or other biochemical assay (red blood cell count, viral load, HbA1c level, etc.), genetic data (presence of a specific genetic mutation), or measurement from an image (coronary artery stenosis, cancer metastases, etc.). (See also intermediate endpoint and surrogate endpoint.)

Reference

Goodman CS. HTA 101: Introduction to Health Technology Assessment. Bethesda,MD: National Library of Medicine (US); 2014.