A chemiluminescence immunoassay for the quantitative measurement of CYFRA 21-1 in serum and heparin plasma.CYFRA 21-1 is a fragment of cytokeratin 19. Although expressed in all body tissues its major occurrence is in the lung, particulary in lung cancer tissues. The major diagnostic importance of CYFRA 21-1 as a tumor marker is in differential diagnosis, prognosis, and aftercare of non-small-cell lung cancer (NSCLC) patients. Additionally, CYFRA 21-1 has been described as a tumor marker for the monitoring of bladder cancer. The DRG CYFRA 21-1 CLIA uses the two mouse monoclonal antibodies KS19.1 and BM19.21 to determine cytokeratin 19 fragments.The DRG CYFRA 21-1 CLIA is a chemiluminescence immunoassay (CLIA), based on the sandwich principle. The microtiter wells are coated with a monoclonal [mouse] antibody directed towards a unique antigenic site on the CYFRA 21-1 molecule. An aliquot of sample containing endogenous CYFRA 21-1 is incubated in the coated well with enzyme conjugate, which is an anti CYFRA 21-1 antibody conjugated with horseradish peroxidase. After incubation the unbound conjugate is washed off. The amount of bound peroxidase is proportional to the concentration of CYFRA 21-1 in the sample. After addition of the substrate solution, the intensity of emitted light is proportional to the concentration of CYFRA 21-1 in the sample.