A radioimmunoassay for measurement of serum thymidine

A simple and sensitive radioimmunoassay for the measurement of serum thymidine has been developed based on the competition between thymidine and an analog (¹²⁵IUdR) for sites on anti-thymidine antibody. Antibody-bound ¹²⁵IUdR was measured in ammonium sulfate precipitates. None of the structurally related compounds that are normal body metabolites showed thymidine's ability to displace the label except at 200-fold higher concentration. A thymidine concentration of slightly greater than 10^?6m has been measured in mouse blood serum. The rate of disappcarance of a thymidine load from the bloodstream has been followed after intravenous administration. The sensitivity and specificity of the technique have been discussed, and applications in radiotherapy and chemotherapy depending on altered DNA synthesis or cell death have been suggested.