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3 Dec
Clinical care

Celebrating a newborn screening test milestone

3 December 2019

For over 50 years the lives of thousands of babies have been improved through a simple blood test.

The newborn heel-prick test, or Guthrie test, is now used all over the world, and 2019 marks 50 years of its use in New Zealand. The test is used to screen newborn babies for over 20 rare conditions, including cystic fibrosis.

The screening tool was developed by American doctor Robert Guthrie who initially used it as a cheap way to screen babies for the inherited metabolic condition phenylketonuria (PKU). PKU is caused by a defect in the gene that helps to create the enzyme needed to break down phenylalanine. Phenylalanine is found in many foods, especially protein, and if it can’t be broken down it can cause seizures, delayed development, hyperactivity and other problems.

In New Zealand the Guthrie test was used in some hospitals prior to 1969, but in 1969 the Health Research Council provided a grant to start newborn screening, and the National Testing Centre was established at the Otago Medical School.

In the late 70’s CFNZ patron Professor Bob Elliot made a major worldwide breakthrough in how to easily and quickly diagnose cystic fibrosis. He used old Guthrie cards and determined his new blood test was 100% effective in diagnosing cystic fibrosis. This meant vital early treatment could be started before irreversible scarring of the lungs occurred.

“It’s been impossible to prove what benefit the newborn screening has imparted [for cystic fibrosis] as it’s not ethical to screen and only tell half of those detected they have the disease. There is indirect evidence of course,” Professor Elliot says.

“The age of diagnosis in the USA before screening was about 18 months, which fell to 2 months after screening was introduced. Median survival rose from 7–10 years to more than 40 years,” he says.

“I think we still haven’t taken full advantage of early diagnosis by being more proactive in introducing known beneficial treatments from the time of diagnosis. This will be even more important as new treatments come along.”

“My informed guess [of the impact] of newborn screening is that it has added 30 years of life for people with CF, and hopefully more [years] to come,” Professor Elliot says.

Screening for cystic fibrosis in New Zealand has been included as part of the routine Newborn Metabolic Screening Programme since 1986. The test measures the level of an enzyme called immunoreactive trypsinogen (IRT) which can be elevated in babies with cystic fibrosis.

Trypsinogen is produced by the pancreas and travels to the small intestines where it’s converted to trypsin and is responsible for breaking down protein in food. Without enough trypsinogen and trypsin, the body can’t digest and use protein properly.

When a baby is born with cystic fibrosis their pancreatic ducts can become blocked with mucus and blocks the trypsinogen from getting to their intestines leading to an elevated IRT level.

Many other cystic fibrosis related medical breakthroughs have changed the way CF is treated and improved people’s quality of life. With precision medicines and ongoing research we continue to look forward to the time when CF means cure found.

Read the Ministry of Health news article celebrating the milestone

Watch six videos about families who have benefited from metabolic screening, including 2-year-old Otis who has cystic fibrosis. Watch the videos


  1. Newborn metabolic screening, Ministry of Health
  2. Phenylketonuria, Mayo Clinic 
  3. Guthrie Tests, Privacy Commissioner 
  4. Our Breakthroughs, Cure Kids 
  5. Newborn Screening and Diagnostic Protocol for Cystic Fibrosis in New Zealand, National Screening Unit 
  6. Immunoreactive Trypsinogen (IRT) Lab Tests Online