Serum deoxythymidine kinase: no help in the diagnosis and prognosis of monoclonal gammopathy.

Serum deoxythymidine kinase activity (S-TK) was determined in the diagnostic evaluation and follow-up of patients with monoclonal gammopathy of undetermined significance (MGUS). During a 4-year period 35 patients were included in the study. Normal concentrations of S-TK were found in 33. Patients with non-progressive monoclonal gammopathy kept a stable, and for the individual, a characteristic level of S-TK during several years of follow-up. A moderately elevated level of S-TK during observation did not indicate progression. Even in four out of five patients developing symptomatic multiple myeloma S-TK remained unchanged. Determination of S-TK does not give diagnostic or prognostic information in monoclonal gammopathy.