The DiviTum assay determines the enzymatic activity of thymidine kinase in serum samples. In the assay, thymidine is replaced by bromodeoxyuridine (BrdU), which is accepted by thymidine kinase as an analogous substrate:

BrdU + ATP → BrdU-monophosphate + ADP

Thymidine kinase activity determines the amount of BrdU built into a DNA strand. This BrdU incorporation is detected by an ELISA technique. The DiviTum™ technology amplifies the signal, enabling the assay to measure thymidine kinase activity with high sensitivity.