Rapid 2nd-Tier Test for Measurement of 3-OH-Propionic and Methylmalonic Acids on Dried Blood Spots: Reducing the False-Positive Rate for Propionylcarnitine during Expanded Newborn Screening by Liquid Chromatography–Tandem Mass Spectrometry

• DOI: 10.1373/clinchem.2007.087775
• Publication Date: 2007-05-18T17:12:17Z
• Authors: Giancarlo la Marca; Sabrina Malvagia; Elisabetta Pasquini; Marzia Innocenti; Maria Alice Donati; Enrico Zammarchi
• Keywords: Spots; Dried blood spot; Methylmalonic acidemia; Dried blood

Abstract Background: The expansion of newborn screening programs has increased the number newborns diagnosed with inborn errors metabolism in presymptomatic phase, but it also costly, stress-producing false-positive results. Because propionylcarnitine (C3) is one analytes most frequently responsible for results, we aimed to develop a rapid liquid chromatography–tandem mass spectrometry (LC-MS/MS) method identify free methylmalonic (MMA) and 3-OH propionic (3OH-PA) acids blood spots. Methods: We studied spots from 250 healthy controls; 124 infants abnormal C3, whom only 5 (4%) were truly affected; altered isolated methylmalonylcarnitine; 4 clinically patients. Whole was eluted 3.2-mm dried spot by CH3CN/H2O 7:3 mL/L formic. This extract injected into LC-MS/MS equipped pneumatically assisted electrospray without derivatization. Total analysis time min per sample. Results: assays linear up 3300 nmol/L both metabolites. Intra- interassay imprecision data 3.6%–8% 3.1%–6%, respectively, MMA 5.2%–20% 3.6%–17% 3OH-PA. Limit detection limit quantitation 1.95 4.2 μmol/L, 8 10 μmol/L recoveries 92.9%–106.1%. No deterioration noted on columns after 500 chromatographic runs. If new had been used as 2nd-tier test samples, true positives would have recalled additional positive predictive value 100%. Conclusions: potential markedly reduce results associated costs anxiety. It may be suitable diagnosing routinely monitoring aciduria acidemia.