Our DART and Bioanalytical Chemistry teams have partnered to broaden the scope of fetal rat assessments with the successful validation of T3 (triiodothyronine) and T4 (thyroxine) concentration assays for late fetal (gestational day 20) and early neonatal (postnatal day 4) rat serum. The combined method uses ultra-high pressure liquid chromatography, coupled with a high-end tandem mass spectrometer (UHPLC-MS/MS) for pg/mL level detection.
This exciting development improves upon traditional electrochemiluminescent immunoassays (ECLIA), which have limits of detection (LOD) of 408.9 pg/mL (T3) and 546 pg/mL (T4). Because fetal specimens generally fall significantly below these levels, our bioanalytical scientists in Ashland, OH have sought a more sensitive method for assessment. Their work has resulted in the successful development and validation of an LC-MS/MS method for T3 and T4 with lower limits of quantitation (LLOQ) at 5 and 125 pg/mL, respectively (LODs of 2 and 10 pg/mL, respectively), thereby allowing for effective monitoring of neonatal concentrations.
As an added advantage, the single LC-MS/MS assay measures both hormones, thus limiting the required total sample volume to 50 μL for both tests. Charles River continues to offer radioimmunoassay measurement of TSH (LLOQ 2.0 ng/mL), which can be performed on the same sample used for T3 and T4 analysis.