Changes of serum thymidine kinase in children with acute leukemia

Thymidine kinase (TK) is involved in nucleic acid synthesis and is therefore considered to be an important proliferation tumor marker. Our main goal was to determine the significance of elevated TK levels as a relapse marker during follow-up with child patients suffering from acute leukemia.

TK serum levels in 38 children with acute leukemia (34 lymphoblastic, 4 myeloblastic) were determined using radio-receptor analysis (RRA, Immunotech, Prague, USA). All patients included in this study had had TK examined before the start of the treatment and at least twice during the follow-up.

Our results showed that TK serum levels at the time of diagnosis were extremely high (78-5826 U/l, median value 403 U/l, normal < 8 U/l), while in remission TK serum levels were much lower (5-80 U/l, median value 31 U/l). During relapse of acute leukemia (5 cases), TK levels increased considerably to measurements between 120-800 U/l (median value 324 U/l). The study showed that the elevation of TK serum levels during follow-up was a helpful marker for the recognition of an early stage of relapse and in some cases occurred as early as one month before the appearance of clinical signs. Sensitivity in this case was 87% and thus TK serum levels seem to be a very good parameter during follow-up because of acceptable sensitivity, low cost (4 $/sample) and the elimination of a requirement for screening of bone marrow samples.

While TK serum levels were helpful in predicting relapse during follow-up, it is necessary to note that they did not correlate with prognosis in our group of patients during the time of the initial diagnosis of acute leukemia.