Comparison of two methods for the detection of urinary iodine used in epidemiological studies

Two methods for the determination of iodine in urine or serum based on the Sandell-Kolthoff reaction were compared. The first was an autoanalyser method (AAII, Technicon) where the mineralisation takes place in a continuous flow manner. This procedure was used at the Department of Clinical Chemistry of the University Hospital of Berne (Switzerland) from 1968 until 1993. The second method was evaluated and adapted in our own laboratory. Each sample and the iodate-standards are mineralised in a Pyrex glass tube and the decolorisation reaction takes place in a 96-well-microtiter plate which was read by a PC-controlled photometer at 405 nm. This method, with a detection limit of 0.1 micromol/l showed good analytical recovery (90 to 110%) and a low imprecision (intra-assay coefficient of variation (CV) of 5% and an inter-assay CV of 7.5%). In contrast to the autoanalyser method, the microtiter plate-method is suitable both for series up to 24 samples (3-fold) and for single samples. A comparison of 87 samples in the range of 0.1 to 60 micromol/l which were measured with both Sandell-Kolthoff based methods showed no obvious discrepancy. These two methods showed a good agreement for the determination of urinary iodine. This guarantees that the results of earlier epidemiological studies can be compared with recent studies performed in our and many other laboratories.