Positive Newborn Screen for MCAD -- Now What?

Stephanie L. Austin, MS, MA; Laura A. Stokowski, RN, MS


July 10, 2014

Editorial Collaboration

Medscape &

The Positive Newborn Screen: Notifying the Parents

In this situation, a direct phone call from the provider is in order, for several reasons. First, it is essential to ensure that the infant is not showing any symptoms that would necessitate an urgent evaluation. If the parents give a reliable report that the baby is feeding well, sleeping normally, and not exhibiting any unusual behavior (vomiting, diarrhea, flaccidity, lethargy, irritability, inconsolable crying, etc.) or any evidence of an infection, then the parents can be instructed to bring the infant in the following day. In the meantime, they should make sure that the baby feeds every 3-4 hours, going no longer than 4 hours between feedings, including during the night. If the parental report suggests symptoms of a metabolic disorder or an illness, a same-day visit must be scheduled, or if that is not possible, an evaluation in the emergency department. Waiting until the next well-baby check is inappropriate. The provider cannot be certain that the parents will comply and bring the infant in at that time, or the baby might have mild symptoms that are unrecognized by the family.

After learning of the positive screening test, an evaluation of the infant by a pediatric provider must take place. If the infant is symptomatic, admission to the hospital will be required, and confirmatory testing can take place at that time. Otherwise, it can take place on an outpatient basis.

The second reason for contacting the parents directly is that hearing about a possible abnormality on the newborn screen, with even the suggestion of a genetic diagnosis, produces extreme anxiety in some parents.[1] It is difficult to predict which parents will react with a high level of concern and will need further explanation and reassurance.[1] Having your staff report the results to the parents is not ideal because this may not adequately address the parents' anxiety or reassure you that the baby is asymptomatic. Before the parents start seeking information on the Internet that can increase their anxiety, they need to hear the facts from a trusted provider -- that the newborn screening test result isnot a diagnostic test.

Studies show that initial communication about positive newborn screening results is frequently considered unsatisfactory by parents.[1,2,3,4] Sensitive and effective communication directly from the provider to the family is advised.[2] A simple, clear explanation of the meaning of the screening result should include the possibility that the result could be a false positive and what steps will be taken to confirm or rule out a metabolic disorder. Parents will need to know what follow-up tests will be done, how long it will take to receive confirmatory results, who will notify them and how, and what they should do in the meantime, if anything. Some parents will want more information and support than others, so this should not be a rushed communication.

The possibilities presented by an elevated C8 level on the initial newborn screen are:

  • False positive (premature, low birth weight);

  • True positive: infant has MCAD deficiency; or

  • Infant is a carrier of MCAD deficiency.

False-positive results. The low positive predictive values inherent in screening for multiple independent diseases of low prevalence make false-positive results unavoidable.[5] The more screening tests are performed, the more false-positive results can be expected.[6]

The test for MCAD deficiency using C8 as the metabolic marker by tandem mass spectrometry is highly sensitive and specific and produces a low rate of false-positive results.[7] This rate varies among screening programs because of differences in acylcarnitine analysis and profiling.[8] Programs that screen for MCAD deficiency but not other fatty acid oxidation disorders often limit their analysis to octanoylcarnitine, the predominant marker for MCAD deficiency. However, octanoylcarnitine is not specific for MCAD deficiency, and other disorders (such as glutaric acidemia type II) can cause elevations.[9] Thus, newborn screening programs may include additional informative markers, such as the C8 to C2 and C8 to C10 ratios, in the algorithm for detecting MCAD deficiency to increase the specificity of the test.[10] In a review of 33 infants with initial C8 values higher than 5.0 µmol/L, all 33 infants were eventually diagnosed with MCAD deficiency.[11]


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.