Development of a radiotransporter assay for determination of iodide: preliminary studies

The principle of the radiotransporter assay (RATRA) is that the concentration of the substance to be assayed (analyte) is determined by the degree of its competitive inhibition of the binding of radioactive analyte with transporter.

To illustrate this approach, the iodide concentrations in urine samples were determined by means of RATRA using Na+/I- symporter (NIS).

Iodide concentrations ranging from 9 x 10(-6) to 9 x 10(-4) mol/l could be measured without any significant interference of 0.85 mol/l NaCl. The mean recovery rate of added iodide to urine was 96.5%, serial dilutions of urine samples gave almost straight dose response lines passing near the zero point, the mean within assay coefficient of variation (CV) was 8.8% and between assay CV was 12.9%. Although urinary iodide concentrations determined by RATRA correlated with those using a chemical method (r = 0.97) and an electrode method (r = 0.85), there were discrepancies in absolute values particularly at the low level among these.

The RATRA may have a limitation with respect to the specificity for determining analytes in the biological materials, but we suggest it has the ability to detect some factors influencing the transport.