Abstract:Objective: To investigate the combined application value of tandem mass spectrometry (MS/MS) and high performance liquid chromatogram-tandem mass spectrometry (LC-MS/MS) in the newborn screening of children with methylmalonic acidemia (MMA). Methods: The dried blood spot samples from the newborn with abnormal propionylcarnitine (C3) or C3/acetylcarnitine (C2) or C3/free carnitine (C0) levels in the preliminary screening of MS/MS were collected, and the concentrations of MMA, methylcitric acid (MCA) and homocysteine (Hcy) in these samples were detected with LC-MS/MS. The neonates with increased MMA, MCA or Hcy levels were recalled, and their urinary organic acids were analyzed with gas chromatographic mass spectrometry (GC/MS). Last, gene mutation analysis was performed to make a definite diagnosis. Results: A total of 423 samples with abnormal C3 or C3/C2 or C3/C0 levels in the newborn screening were collected, and the positive rate of preliminary screening was about 1%. The LC-MS/MS results showed that 8 neonates had higher MMA and tHcy levels. The GC/MS results further showed that the level of MMA increased slightly. Conclusion: The combined application of MS/MS and LC-MS/MS may increase the positive predictive value and decrease the false positive rate of MMA screening in the newborn, which may have an important clinical significane in the screening of inherited metabolic disorders.