One of the most common screening tests that occurs every day is the PKU blood test. It is administered to newborns in order to test for phenylketonuria and is a mandatory screening in all 50 states of the US. PKU is a condition that has a highly likelihood of causing brain damage and intellectual disabilities when left untreated. Children with PKU can have a difficult time eating and may develop a rash that looks similar to eczema.
PKU is an inherited condition that forces individuals with it to avoid phenylalanine consumption. It’s found in many foods and requires an enzyme to break it down. People with PKU don’t have this enzyme, so phenylalanine levels can build up and cause damage. The links to brain damage and PKU has been known since 1930 and is the first genetic screening blood test that was conducted on infants.
When Is the PKU Blood Test Taken?
Most hospitals or medical providers will have the PKU blood test happen within the first 2 days of life. The newborn’s heal will be pricked so that the blood test can be conducted. It is then sent to a lab to determine if PKU is present. Most children will have a negative test result and go on to live long, fulfilling lives.
If the PKU test is positive, then treatment must begin right away to eliminate the possibility of developmental problems. Low-protein diets that are carefully controlled become a way of life so that the newborn is protected during the first few critical weeks of development. This diet will then be extended to other foods once a child is able to chew.
Some countries do not screen for PKU at birth, so parents who are adopting children from other nations may need to have a PKU blood test conducted to determine if the condition is present. Screening for other genetic illnesses typically happens at the same time as the blood test to limit the discomfort of the child.
What Do the Test Results Mean?
Every lab has what they consider to be a different “normal” value. In general, however, the normal levels of phenylalanine that are in the blood are less than 2 mg/dL. When a blood test result comes back as having more than 4 mg/dL, or double the normal amount, then the medical provider will suspect that PKU may be present and recommend a treatment protocol. A retest will generally be ordered in 7-14 days to confirm the outcome.
Sometimes false positives or false negatives may result under specific circumstances. A child that has taken aspirin for some reason, though not recommended, may have a false result. Antibiotics that are administered to a newborn will also cause false results.
Children who are born premature and have liver enzymes that are not fully developed will also have a higher likelihood of a false negative outcome. Children with feeding problems may also experience a false negative if they are routinely vomiting. There is some thought that children shouldn’t be tested for PKU until they’ve been feeding for several days.
Mothers who are breastfeeding should let their medical provider know of their lifestyle habits as certain medications, supplements, and vitamins may also affect the results.
What About Mothers Who Have PKU?
For mothers who are trying to become pregnant or have a confirmed pregnancy, a PKU blood test may also be ordered to determine what her phenylalanine levels happen to be. Even if a child does not have the inherited disorder themselves, a mother’s high levels of phenylalanine can still cause brain damage and/or intellectual deficits in the child after birth.
People with PKU must stay on a low-protein diet throughout their lives to avoid health problems that may develop. Children will be drinking milk substitutes that do not contain the normal protein levels. If the PKU blood test was missed for some reason, then there is also a urine test that can be conducted to determine if the genetic disorder may be present.
In the past, there weren’t many actions that could be taken to help treat children with this genetic disorder. Thanks to early testing protocols and knowledge of how phenylalanine affects the body, children today only face the challenge of eating foods that do not build up phenylalanine levels. Every child in the US is supposed to receive this blood test, so it is normal, takes only a few seconds, and the results could save a newborn’s life.