|Newborn Screening by a Non-derivatized Tandem Mass Spectrometry Assay|
|Tue 10:30 AM - Session: Inborn Errors in Metabolism|
|Tandem mass spectrometry has greatly enhanced newborn screening by providing the capability of multiplex measurement of amino acids and acylcarnitines from a single sample and thus enabling the detection of over 30 inborn errors of metabolism. Until recently, conventional methods lacked the ability to include the measurement of Succinylacetone (the primary marker for Tyrosinemia Type I) in their multiplex panel of measurable analytes. Here we report analytical and clinical results of a Non-derivatized tandem mass spectrometry assay that allows the simultaneous measurement of 12 amino acids, 30 acylcarnitines, and succinylacetone from a single sample preparation. Compared to methods that require sample derivatization, the present assay procedure is much simpler requiring only the extraction of the of the sample with a working solution that contains reagents necessary for the extraction of succinylacetone as well as stable isotope internal standards for the quantitation of the analytes of interest.
Overall, the assay provides excellent analytical performance with linearity ranges that cover all clinically relevant analyte levels, total imprecision (%CV) at the clinically significant levels in the single digits to low teens and adequate recovery to ensure the appropriate sensitivity for the assay. Additionally, comparison to a well established derivatized method indicates that avoiding the derivatization step does not have a deleterious effect on the performance of the assay. Further, the analytical performance of the assay was verified at three newborn screening sites demonstrating the appropriateness of the assay for newborn screening settings.
The clinical performance of the assay was verified by the analysis of actual neonatal dried blood spot samples at three different newborn screening sites. In total, more than 11,000 neonatal samples were analyzed including over 10,900 random presumptive negative samples and 118 true positive samples representing 18 different inborn errors of metabolism. In all cases, the non-derivatized assay was able to identify the correct disorder represented by the true positive samples. In addition, the analysis was performed in parallel to the derivatized assay at two of the three sites where ~8400 presumptive negative and 104 true positive samples were measured in a paired manner with and with out derivatization. Overall, the agreement between methods is excellent with percent agreement between paired samples of 90% or better in terms of clinical determinations. Special emphasis is placed on the analysis of five Tyrosinemia Type I samples highlighting the advantages of screening for this disorder using succinylacetone as the primary marker instead of tyrosine.