A primer on expanded newborn screening by tandem mass spectrometry

Newborn screening (NBS) for a wide variety of inborn errors of metabolism using the powerful tool of tandem mass spectrometry (MS/MS) is becoming widespread. This article provides the basic information that primary care clinicians need to help make rational decisions about urgent evaluation and appropriate follow-up of patients with abnormal expanded NBS tests. Also outlined are ways that the screening tests can be inaccurate. A normal MS/MS NBS result does not rule out the possibility of an inborn error of metabolism in an infant with acute illness, developmental abnormalities,or other clinically suggestive conditions. Primary care practitioners should identify the metabolic specialists in their area and develop a relationship with them to ensure clear communication when abnormal results arrive. Included in this article is a catalog of "thumbnail sketches" for reference by physicians when they receive an abnormal MS/MS NBS result.