Newborn metabolic screening is one of the largest programmes in New Zealand and each year over 60,000 newborns are screened for 28 metabolic disorders. Approximately 45 babies are found each year to have one of the disorders.

Newborn metabolic screening is one of the great successes of public health screening. Around the world it has lead to many thousands of children being protected from intellectual disability and death.

Metabolic disorders are measured in incidence rates - that is the number of people diagnosed with one of the disorders. The disorders, cause, treatment and incidence rates for New Zealand are as follows:

Disorder	Cause	Treatment	Incidence/number of babies diagnosed per year in NZ
Congenital hypothyroidism	The thyroid is missing, not functioning or in the wrong place. Can lead to slow growth and developmental delay.	Medication (thyroid hormone)	1 in 4,000 babies approx. 15 babies/year
Cystic Fibrosis	A defective gene and its protein product leads to thick sticky mucus.	Medication Physiotherapy	1 in 7,000 babies approx. 8 babies/year
Amino Acid disorders (14 disorders) e.g. Phenylketonuria (PKU)	An enzyme is missing. e.g. PKU - without this enzyme an amino acid (called phenylalanine) rises to harmful levels and can lead to brain damage.	Special diet	1 in 12,000 babies approx. 5 babies/year
Fatty acid oxidation disorders (9 disorders) e.g. Medium chain acyl-CoA dehydrogenase deficiency or MCADD	An enzyme is missing. Without these enzymes energy cannot be converted from fats and can lead to coma and death.	Regular feeding (avoidance of fasting)	1 in 12,000 babies approx. 5 babies/year
Congenital Adrenal  Hyperplasia (CAH)	An enzyme is missing in the adrenal gland. In severe forms leads to ambiguous genitalia in girls and salt/hormonal imbalances in both sexes.	Steroid   medication	1 in 20,000 babies approx. 3 babies/year
Galactosemia	A defective enzyme prevents normal use of milk sugar leading to jaundice, cataracts and life-threatening illness.	Special diet	1 in 100,000 approx. 1 baby every 2 years
Biotinidase deficiency	An enzyme is missing resulting in a deficiency in biotin. This deficiency can lead to seizures, hearing loss and developmental delay.	Vitamin H (biotin)	1 in 150,000 approx. 1 baby every 3 years

Screening does however have its limitations. It only detects babies who may be at risk of one of the disorders which is why it is always followed by diagnostic testing if required.

For all screening - whether it is newborn metabolic or other screening, there will be false positives and false negatives. A false positive screening test result is one where the result shows there may be a problem when there isn't and a false negative result is one where the result is normal but there is a potential problem. One of the aims of the programme is to reduce these but continue to improve the health and wellbeing of New Zealand children.