Development of radioimmunoassay for human C-reactive protein using magnetizable cellulose particles

A novel Radioimmunoassay (RIA) method was developed for measuring C-reactive protein (CRP) in human serum. The development of CRP-RIA includes CRP radiolabelling with Na¹²⁵I using the Chloramine -T method to prepare ¹²⁵I-CRP tracer and purify it using Sephadex G-25 Column. Polyclonal anti-CRP was coupled with magnetizable cellulose particles with an average particle size of < 2 µm. Two types of assays were developed: (1) An assay with an extended standard range (0–6400 ng/mL), which can measure CRP levels up to 160,000 ng/mL, and (2) A sensitive assay (0–200 ng/mL), which can measure the CRP level in human serum as low as 3 ng/mL. The developed assay procedures were validated after studying standard assay parameters such as sensitivity, assay variations, linearity of dilution, etc. This assay is user-friendly, with only three pipetting steps and a convenient incubation time of 1 h at room temperature. The developed CRP-RIA method covers the entire physiological and clinical useful range for routine estimation of CRP in human serum.