Reduction of the false‐positive rate in newborn screening by implementation of MS/MS‐based second‐tier tests: The Mayo Clinic experience (2004–2007)

Abstract

The continued expansion of newborn screening programmes to include additional conditions increases the responsibility of newborn screening laboratories to provide testing with the highest sensitivity and specificity to allow for identification of affected patients while minimizing the false-positive rate. Some assays and analytes are particularly problematic. Over recent years, our laboratory tried to improve this situation by developing second-tier tests to reduce false-positive results in the screening for congenital adrenal hyperplasia (CAH), tyrosinaemia type I, methylmalonic acidaemias, homocystinuria, and maple syrup urine disease (MSUD). Beginning in 2004, this approach was applied to Mayo's newborn screening programme and resulted in a false-positive rate of 0.09%, a positive predictive value of 41%, and a positive detection rate of 1 affected case in 1672 babies screened.

Dried blood spot sampling in combination with LC‐MS/MS for quantitative analysis of small molecules

“…For example, acylcarnitines are unstable if stored at room temperature for more than 2 weeks on DBS due to hydrolysis, but they are stable for at least 330 days when stored at ≤−18°C . Without establishing the analyte storage stability coverage (from sample collection to analysis), a retrospective reanalysis of the study samples might not be confi rmative for any purpose, especially for newborn screening, for which the confi rmatory analysis (secondtier test) is often conducted, but only after the initial population screening Lai et al, 2001Lai et al, , 2002la Marca et al, 2007la Marca et al, , 2008aMatern et al, 2007). Stability assessment.…”

“…Furthermore, the possible in-source fragmentation in the case that the target analyte is a derivative of another intact biomarker molecule and natural isotope contribution might add another challenge to MS/MS (infusion or fl ow injection) only assays (Garg and Dasouki, 2006;Piraud et al, 2003). Consequently, LC-MS/MS has been increasingly explored in the confi rmatory analysis (second-tier test) of those 'diffi cult' biomarker molecules, resulting in a reduced false-positive rate (Janzen et al, 2007;Lacey et al, 2004;la Marca et al, 2007 and2008a;Matern et al, 2007;Minutti et al, 2004).…”

A Rapid Screening Method for the Measurement of Neonatal Total Homocysteine in Dried Blood Spots by Liquid Chromatography-Tandem Mass Spectrometry

“…The technique is capable of rapidly detecting over 60 disorders within 2 min of analytical time. In addition, several laboratories have implemented a 2nd tier or reflex analysis on the same DBS by LC-MS/MS to measure more disease-specific biomarkers when the primary screening marker's disease range overlaps with the normal range [18][19][20][21]. The Metabolic Laboratory at HMC serves as the national NBS laboratory for the State of Qatar, and aims to further improve NBS procedures by providing more rapid and accurate diagnostic testing procedures to benefit newborns in Qatar, as well as other NBS programs worldwide.…”

Expansion of the Phenotypic Spectrum of Propionic Acidemia with Isolated Elevated Propionylcarnitine

“…PA is included in the NBS core panel, to rule out a subset of C3-related metabolic disorders resulting from propionate accumulation (PA, methylmalonic aciduria (MMA), certain cobalamin (Cbl) disorders). C3 is not specific for PA and a second-tier strategies analyzing methylmalonic acid, 3-hydroxypropionic acid, and 2-methylcitric acid from the initial DBS have been developed (la Marca et al 2007;Lindner et al 2008;Matern et al 2007). Many laboratories use ratios of C3 to other acylcarnitine species (C2, C0, C16) or to methionine to improve specificity and sensitivity of C3 test (Wikoff et al 2007).…”