Rapid and Automated Assay for Thyrotropin in Guthrie Cards on the ACS:180

Abstract

Congenital hypothyroidism causes a decreased growth rate and skeletal development and can lead to severe mental retardation (1). In the nearly three decades since measurement of thyroxine in filter paper dried blood disks (Guthrie cards) was introduced as a method to screen newborns for congenital hypothyroidism (2), new procedures for thyroxine and thyrotropin (TSH), such as ELISA, fluoroimmunoassay, or chemiluminescence (3) have been developed or adapted from commercial kits, most of them requiring overnight incubation. Previously, we described a manual adaptation of a commercial immunochemiluminometric assay kit based on an acridinium label to measure TSH in dried blood spots (4). This method is used routinely in our laboratory, and we have detected 176 congenital hypothyroidism cases in the 480 000 newborn samples tested. Studies concerning its correlation with the DELFIATM neonatal TSH kit (Wallac Oy) were also described (5). Here, we present results obtained with a rapid and automated third-generation TSH chemiluminescent assay for serum samples adapted to measure TSH in Guthrie cards (ACS:180TM, Chiron Diagnostics). This fully automated chemiluminescence immunoassay system uses paramagnetic particles as the solid phase (6). We measured TSH in 2200 dried blood spot samples obtained in filter paper (Schleicher and Schuell, cat. no. 903) by heel stick from newborns routinely referred to our service. The samples were dried at room temperature, and the TSH concentrations were measured using our routine chemiluminescent method (4) and also by the technique described here. We used calibrators at 2.2, 22.0, 55.0, 110.0, 220.0, and 550.0 mIU TSH/L serum equivalent and controls at 33.0 and 132.0 mIU TSH/L serum equivalent provided with the DELFIA …