Thymidine kinase (TK1)
An enzyme involved in making DNA, so its level in the blood rises when cells are dividing rapidly. It is used mainly as a marker of activity in certain blood cancers such as some lymphomas and leukaemias — to help gauge how active the disease is and monitor it.
What it measures
Thymidine kinase (the TK1 form) is an enzyme cells use when they copy their DNA to divide. Because it is produced mainly during cell division, its activity in the blood reflects how much rapid cell proliferation is going on in the body. This makes it a marker of proliferative activity rather than of one specific organ. Its established use is in certain blood cancers — some lymphomas, leukaemias and related conditions — where a higher thymidine kinase level indicates more active, faster-dividing disease, and can help with assessing how aggressive a condition is, gauging prognosis, and monitoring the response to treatment or watching for relapse. It has also been studied as a marker in some solid tumours, but its main practical role is in haematology. Because any state with a lot of cell turnover — including some infections and inflammatory conditions — can raise it, thymidine kinase is not a screening test and is interpreted only within the specialist care of a defined condition, alongside other markers such as LDH.
What a high value can mean
- Active, rapidly proliferating blood cancer — such as some lymphomas or leukaemias; a higher level reflects more active disease.
- A rising trend — can indicate progression or relapse, in a known condition.
- High cell turnover from other causes — some infections and inflammatory states can raise it, so it is not specific to cancer.
What a low value can mean
- A normal or low level is expected outside the conditions it is used for — and, in a monitored blood cancer, can reflect low disease activity or a good response to treatment.
When to discuss with a doctor
Thymidine kinase is a specialist marker used within the assessment and monitoring of certain blood cancers, not as a general or screening test. Where it applies, its value is in reflecting how active and fast-dividing a known condition is, and in following its trend during treatment — a rise can suggest progression or relapse, always interpreted with the clinical picture and other markers such as LDH by a haematologist. Because a raised level can also come from ordinary high-cell-turnover states like some infections, it is never read in isolation. Mediora.AI shows thymidine kinase alongside related markers so the pattern is visible in one place; interpreting it belongs with your specialist team.