Latest Resource: Newborn Metabolic Screening Programme - Best Practice for Health Practitioners

Newborn metabolic screening is one of the largest screening programmes in New Zealand. This 17 minutes DVD outlines your responsibilities as a Lead Maternity Carer and provides best practice guidelines for the programme and the heel prick test.  

• Download and view the Lead Maternity Carers DVD  (.wmv / 23193kb)

Here is further information for LMCs based on questions and comments that we have received both from the DVD release and education sessions the programme has been performing around New Zealand.

Testing requirements

When should the test be taken?

At 48 hours or as soon as possible after this.

Why at 48 hours of age or as soon as possible after this?

 Many conditions do not show abnormal metabolites at birth as the placenta clears them away as the baby’s system produces them (this is the reason babies can be affected but be born without symptoms or signs of disease). The baby, therefore must be independent of mother for long enough for the indicator metabolites to increase. But, the period of starvation babies have after birth (they lose birth weight because they’re not feeding sufficiently to meet their body needs) raises some of the indicator metabolites, especially those used to detect the fatty acid oxidation disorders (see Screening Matters June 2008) which then normalise when baby starts eating well. So the test must be taken late enough for the conditions to be detectable, and early enough for the fatty acid oxidation indicators still to be raised. The optimal time for testing is therefore 48 hours.

Conditions like MSUD, galactosemia and CAH can be fatal within 7-10 days so it is also very important to send the cards to the laboratory as soon as they are dry to ensure testing is completed early enough to give clinical benefit if one of the disorders is identified.

Do antibiotics affect the test?

No.

Originally screening tests were bacterial inhibition assays. When a baby was on antibiotics the screening test didn’t work and had to be repeated when the baby had completed a course of antibiotics. In the early 1980’s the programme began using an alternative way of measuring aminoacids (TLC) and antibiotics haven’t been a problem since that time.

Do stools need to change prior to testing?

No.

We’re not absolutely sure where this came from. It may be from a research study done in the late 1970’s looking at faecal chymotrypsin as an indicator metabolite for cystic fibrosis screening. The programme has been screening for Cystic Fibrosis using blood immunoreactive trypsin since the early 1980’s. This is not at all affected by the appearance of the baby’s stools.

How much milk/protein feeding is needed?

None.

In the early period of screening it was thought that babies needed protein feeding to raise the aminoacids used to screen for PKU and MSUD. It has gradually been realised that as babies lose birthweight, they break down body protein and this will raise the indicator metabolites in aminoacid disorders. In addition, new technology (tandem mass spectrometry) enables the measurement of more than one indicator for each condition and this makes screening more sensitive and specific. For example, PKU screening measures both phenylalanine, the substrate and tyrosine, the product of the enzyme, phenylalanine hydroxylase that is missing in PKU. So, the baby needs to be old enough for the indicator metabolites to increase but doesn’t need any particular amount of protein feeding.

Information for parents and non health-pracitioners can also be found on this website.