Frequently asked questions
The blood spot sample must be taken when baby is 48 hours old, or as soon as possible after this, and before they are 72 hours of age.
When the baby is in utero, it is nourished by the placenta and has all its needs met by the mother. Many disorders do not show abnormal biochemical levels at birth because the placenta eliminated them as the baby’s system produced them. This is why babies may be affected by a disorder, but born without signs or symptoms.
For effective newborn metabolic screening, the baby must be independent of the mother long enough for the indicator biochemicals to show an abnormality. For fatty acid oxidation disorders, the catabolic state babies experience after birth (when they lose birth weight because they are not feeding sufficiently to meet their body needs) changes the indicator biochemicals. The fatty acid biochemicals normalise when baby starts eating well. In other disorders (eg, amino acidopathies) the biochemicals will continue to be abnormal and some will rise to toxic levels.
The sample must be taken late enough for the disorders to be detectable, and early enough for the fatty acid oxidation indicators still to be raised. The optimal time for measurement of the different biochemicals is 48 hours.
Once the sample has been taken, laboratory testing should be carried out as soon as possible.
Originally, screening tests were bacterial inhibition assays. When a baby was on antibiotics the screening test did not work and had to be repeated when the baby had completed the course of antibiotics. In the early 1980s the programme began using an alternative way of measuring amino acids (TLC) and antibiotics have not been a problem since that time.
In the early period of screening it was thought that babies needed protein feeding to raise the amino acids used to screen for PKU and Maple Syrup Urine Disease (MSUD). It has now been realised that as babies lose birth weight, they break down body protein and this will raise the indicator metabolites in amino acid disorders. In addition, new technology (tandem mass spectrometry) enables the measurement of more than one indicator for each disorder 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.
The baby needs to be old enough for the indicator metabolites to increase but doesn’t need any particular amount of protein feeding.
The laboratory which performs the screening for the programme must be IANZ accredited against the international standard ISO 15189. This is the highest accreditation programme available. IANZ stands for International Accreditation New Zealand. Accreditation by IANZ ensures that the laboratory that carries out these tests is technically competent, has appropriate processes and is using appropriate up-to-date technology. It is an internationally recognised process for assessing the technical competence and effective quality processes of a professional service (in this case a medical testing laboratory) and its staff.
Accreditation involves checking that the laboratory has processes to ensure staff are adequately trained and competent in the tasks they perform; that equipment is regularly maintained and has functional checks before each use, and that there are robust processes for tracking specimens, testing and reporting. Overseas experts are regularly brought in to ensure New Zealand processes are of a similar standard to elsewhere in the world.
Part of checking the quality of testing involves ensuring that the laboratory has satisfactory performance on external (the laboratory participates in programmes from the Centre for Disease Control in America and other external programmes) and internal quality assurance programmes. For further information see the IANZ website.
After testing, the residual blood spots are stored indefinitely in a secure locked area, or returned to the parents/guardians or individual if requested. Parents/guardians or individuals can request the return of their blood spots at any time, using the 'Return of newborn metabolic screening samples (Guthrie Cards) to family' form.
Only authorised staff from the screening programme can access stored blood spots.
When a heel prick is performed information is provided on the card. This information includes demographic data (for example the baby's name, sex, birth date, time, weight, the mother’s details and LMC details). This data is entered into a secure information system. Once screening is completed the results of the tests are also captured in the information system. The data is used for screening purposes and is only accessed by authorised personnel. Data is provided to the Ministry of Health for monitoring, evaluation and reporting.
Stored blood spots may be used for:
- for repeat testing. If a baby has a disorder but did not have a positive screening result, the blood sample can be tested again to see why this happened
- to improve the screening programme
- to investigate a death or illness in a family
- for victim identification, governed by a Memorandum of Understanding with the New Zealand Police
- for research approved by an ethics committee.
Stored blood spot samples cannot be used for identification of criminals, unless there is a court order. This has never occurred in the history of the Programme.
The NSU has a Memorandum of Understanding with the New Zealand Police regarding disclosure of this information. The Ministry of Health and the New Zealand Police first signed the Memorandum of Understanding in 2006. The Memorandum was reviewed in 2013 with the framework for police requests for access to the blood spots becoming Schedule 2, signed in May 2014.
To date, blood spot cards have not been used for large scale population studies.
As part of metabolic screening, about 1 percent of samples are tested for a change in DNA (mutation) associated with cystic fibrosis. No other DNA testing is done on samples unless authorised by the parents/guardians/individual or through legal avenues, such as a court order.
The Policy Framework sets out the requirements for population research studies. These include:
- the study must have ethics committee approval
- the study must have Ministry of Health approval
- the study must be presented to the Programme Governance Team
- the research may not use up all the blood on an individual's card
- the research must be considered an appropriate use of residual blood spot samples and contribute to the public good through increased scientific knowledge.
The Newborn Metabolic Screening Programme screens for over 20 metabolic disorders.
For more information and a full list of disorders see About the Test.