Radioimmunoassay for serum apolipoprotein D, an atypical apolipoprotein: validation and clinical application.

Apolipoprotein D (apoD) is an atypical apolipoprotein in terms of its structure, synthesis and probable function. It is the most abundant protein in breast cyst fluids of patients suffering from macrocystic disease of the breast, a disease associated with an increased risk of developing breast cancer. We have developed and optimized a competitive radioimmunoassay for the measurement of apoD in human serum. The assay uses a solid phase separation method and with a 4 h incubation period, it can be completed in a single working day. The within and between run coefficients of variation were < 8.5% and < 12.2%, respectively, and quantitative recovery of apoD was obtained over the range 250-5000 micrograms/L. There was no difference in the serum concentrations of apoD between female controls, patients with benign breast disease and early breast cancer. However, serum apoD was significantly lower in breast cancer patients with bone metastasis.