[Clinical evaluation of a lung cancer-associated protein antigen, cytokeratin 19 fragment: II. Radioimmunoassay and effect of aging and smoking over serum level of normal individuals].
Serum level of cytokeratin 19 fragment which is a tumor associated antigen of lung cancer was detected by the radioimmunometric assay. Effect of smoking and of aging on serum reference value was analyzed over 331 normal individuals. Serum cytokeratin 19 fragment level of smokers, mean 0.89ng/ml, was higher than that of non-smokers, mean 0.70ng/ml although there was no statistical meaning over the difference. And there was tendency to increase of cytokeratin 19 fragment level with aging. Mean + 2SD of cytokeratin 19 fragment of normal was 2.17ng/ml. Clinico-epidemiological specificity of cytokeratin 19 fragment on normal individuals was discussed.