Tandem mass spectrometry screening is a test that screens newborns at birth for genetic disorders. Newborns are born with a newborn screening test, usually three drops of plantar blood, for hypothyroidism and phenylketonuria. The tandem mass spectrometry test, which also involves collecting plantar blood, checks for 26 diseases. Tandem mass spectrometry screening is the newest method of newborn screening, which focuses on 48 genetic metabolic disorders including abnormal amino acid metabolism, organic acid metabolism disorders and fatty acid oxidation defects.