What it measures
The test looks for cells that have broken away from a solid tumour and are travelling in the bloodstream. Labs separate them from the far larger number of normal blood cells and identify them by markers on their surface. Methods differ widely between labs.
Why people test it
- Offered privately as a blood test that looks for cancer cells in the bloodstream.
- Used in research and some specialist clinics to follow cancers that have spread.
Typical range
Results are reported as detected or not detected, sometimes with a count of the cells found in the sample. Methods and cut-offs differ between labs, and the report explains how the lab reached its result.
Finger-prick or vein?
A vein sample is needed. These tests need more blood than a finger prick gives, often in special tubes that keep the cells intact.
Circulating tumour cell tests are not part of any NHS screening programme, and a result is not a diagnosis. Discuss your result with your GP.