New Zealand babies will be tested for rare and life-threatening Severe Combined Immunodeficiency at birth from next year.
The exact number of babies who a born with the disease is hard to quantify because it's often fatal before diagnosis, according to Health Minister Jonathan Coleman.
SCID is the name for a number of rare diseases where genetic defects prevent the normal development of cells needed for immunity.
"Most babies with SCID appear healthy at birth and aren't diagnosed until six to nine months of age. If untreated, it can be fatal within the first year of life," he said.
Early detection through metabolic screening will allow doctors to treat patients with stem cell transplants.
The test is expected to be implemented into the newborn metabolic screening programme by the middle of next year.