Introduction. Newborn screening is a population-based system for the identification and early treatment of potentially devastating medical conditions. In the United States, this screening is mandated in every state, but the disorders included in the screening panels vary. A list of the screening tests provided by each state can be found on the "Peristats" section of the March of Dimes website at http://marchofdimes.com/peristats or at the National Newborn Screening and Genetics Resource Center website at http://genes-r-us.uthscsa.edu. An expert panel commissioned by The American College of Medical Genetics has recommended 29 conditions on newborn screening panels (Table 14–1).
Screening of infants cared for in the neonatal intensive care unit (NICU) can present special challenges. Underlying medical conditions, including prematurity, can impact the validity of the screening results, as can some of the therapies provided in the NICU. Regulations related to follow-up of screening specimens vary from one state to another, and information on optimal methodology and timing of screening is incomplete for many disorders.
Timing. It is recommended practice to obtain a specimen prior to blood transfusion if a specimen has not already been sent; otherwise an initial specimen is typically drawn between the third and fifth days of life. Any results judged to be invalid by the performing laboratory or any results that are reported as positive must have a repeat specimen. This chapter addresses selected disorders included in most state newborn screen panels, as well as special considerations related to discharge planning and follow-up.
Selected disorders included in newborn screening panels
Amino acid metabolism disorders
Screening process. Increased concentrations of phenylalanine in the blood can be detected using the Guthrie bacterial inhibition assay (BIA), fluorometric analysis, and tandem mass spectrometry (sometimes referred to as MS/MS). It is important to note that antibiotic administration interferes with validity of test results only if the Guthrie BIA is the testing modality used.
Follow-up. Children diagnosed with PKU should receive diets with reduced phenylalanine. Subspecialty follow-up should be arranged with a nutritionist as well as with a pediatrician who specializes in metabolic disorders.
Maple syrup urine disease (MSUD)
Screening process. Tandem mass spectrometry is the screening tool of choice.
Follow-up. Positive screen results should be followed by plasma amino acid analysis. Diagnostic findings include elevated branched-chain amino acids, low levels of alanine, and the presence of alloisoleucine. Children with MSUD should receive follow-up care by a pediatrician who specializes in metabolic disorders, as well as a nutrition consultant.
Screening process. HCY is multifactorial and involves interference in the pathway that converts methionine into cysteine. If untreated, the disease manifests with recurrent thromboembolic events and can lead to mental retardation, as well as ocular and skeletal problems. Screening may be done by a bacterial inhibition assay or tandem mass spectrometry. There may be an increase in false-negative screening results if protein intake via feedings is not adequate.
Follow-up. Increased levels of methionine on screening require follow-up with serum or plasma amino acid levels to ...
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