Guthrie Blood Test Results Interpreted


The Guthrie blood test is a basic screening test that is used to detect phenylketonuria, which is commonly known as PKU. This is the neonatal heel prick test that is performed on newborns as part of the post-birth screening process. The blood soaks into the pre-printed collection cards, which are called Guthrie cards, and has been a standardized process for more than 50 years in Europe and North America.

The blood samples are used for PKU, which is a disorder when amino acid metabolism immediately impairs brain development. Without immediate treatment, an infant suffering from PKU may only survive for a few days.

The Guthrie blood test samples that are taken will also be used to detect several additional genetic conditions that are important to begin treating right away. Here are the results which may be communicated to new parents after the blood test results are offered.

1. Galactosemia.

This disorder is a rare genetic condition which causes a person’s body to not metabolize galactose properly. For those who are of European ancestry, the birth rate of this genetic disorder is about 1 in 60,000 births. For those within the Irish Traveler population, the birth rate is about 1 in 480 for this disorder.

2. Immunoreactive Trypsinogen.

This part of the Guthrie blood test sample is used to detect the presence of cystic fibrosis, or CF. CF is an inherited disorder that most often affects the lungs, but it can also affect the kidneys, liver, and other organs. Health concerns from CH include difficulty breathing, poor growth, clubbing of the digits, and organ-specific symptoms. There can be varying degrees of cystic fibrosis, with a birth rate for this disorder of 1 in 3,000. About 1 in 25 people are believed to be a carrier for CF.

3. MSUD.

Sometimes called Branched Chain Ketonuria or Maple Syrup Urine Disease, this rare disorder causes the body’s metabolism to inhibit the breakdown of leucine, isoleucine, and valine. These amino acids, when they are not properly broken down, can impair brain development in a similar way to PKI.


This disease is a disorder of the fatty acid oxidation so that the body struggles to break down medium-chain fatty acids. Without a timely intervention, this disease is known to bring about hypoglycemia and sudden death. The health issues of this disease are usually discovered after periods of vomiting or fasting. This genetic disease is found with an incidence rate of up to 1 in 4,000 live births around the world.

5. Sickle-Cell Disease.

Children suffering from this disorder may have one of several different sickle-cell traits that were inherited from their parents. The most common abnormality that is seen is called sickle-cell anemia, which changes the shape of the red blood cell to more of an “S” shape instead of a round shape. This causes some of the cells to stick from time to time, which can cause painful attacks. More than 3 million people are known to have this disease, with it most common in people with an ancestry from sub-Sahara African, India, and the Arabian Peninsula.

When Is the Guthrie Blood Test Given?

The blood sample is generally taken on the fifth day after birth, although there may be exceptional circumstances which require a change in this schedule. Sometimes this test is done for screening purposes within the first day or two of life, but there have been some false positives or false negatives reported on the screening tests if it is performed too early.

This blood test may also be given in conjunction with other tests to determine overall newborn health. A urine test is commonly administered around the same time, with urine from the diaper being applied to filter paper and then tested to see if there are potential health concerns which will need to be addressed.

Here’s What You Need to Know

In most areas of Europe and the United States, the Guthrie blood test is mandated by law to be given after birth. If new parents are immediately discharged from the hospital, an order for a return to have the test administered will be given and an appointment set. A failure to show up for this appointment may result in a family investigation regarding child protection issues.

This also applies to parents who have at-home births or are assisted by a midwife or other professional. The newborn must be taken to a hospital or authorized clinic so this testing can be performed. Failing to do so may also initiate an investigation.

The purpose of this testing isn’t to interfere with family preferences. It is to provide information about the health of the infant so that appropriate treatment measures can be taken if necessary. For additional questions about this test or any other newborn screening, be sure to speak with your medical provider or OB/GYN.