Two tier analysis of organic acid disorders: a comprehensive approach for newborn screening

Abstract

Background: The present study aims at two tier analysis for diagnosis and confirmation of organic acidemia using simultaneous analysis of dried blood spot (DBS) carnitine profile by tandem mass spectrometry (TMS) and urine metabolic analysis on gas chromatography mass spectrometry (GC/MS). Material and Methods: This cross sectional study included 348 DBS samples and their dried filter paper urine sample came for routine and emergency screening of inborn errors of metabolism (IEM). All DBS samples were anlysed for amino acid and acylcarnitine profile derivatized on TMS. All these cases were simultaneously tested for urine organic acid pattern on GC/MS which involved urease pretreatment, deproteinisation followed by derivatisation. Confirmation of IEM was based on the two tier approach containing the blood and urine metabolic pattern as recommended by panel of American College of Medical Genetics (ACMG). Results: 17 cases were screened positive for IEM analysed separately for amino acid /acylcarnitine profile and urine organic acid profile. However the two tier testing screened and confirmed 8 cases of organic acidemia within 36 hours of receipt of sample which included 2 cases each of maple syrup urine disease (MSUD), glutaric acidemia Type I (GA I), and ?-ketothiolase deficiency (BKT) and one each case of multiple carboxylase deficiency (MCD) and propionic acidemia (PA). Conclusion: The simultaneous two tier metabolome testing for screening of IEM is more comprehensive, cost effective, delivering confirmatory results with significantly reduced turnaround time, thus reducing recall rate by eliminating false-positive results and helps prevent unnecessary anxiety of parents.