What is a phenylalanine blood test?

Serum phenylalanine screening is a blood test to look for signs of the disease phenylketonuria (PKU). The test detects abnormally high levels of an amino acid called phenylalanine.

What does high phenylalanine mean?

A dangerous buildup of phenylalanine can develop when a person with PKU eats protein-rich foods, such as milk, cheese, nuts or meat, and even grains such as bread and pasta, or eats aspartame, an artificial sweetener. This buildup of phenylalanine results in damage to nerve cells in the brain.

How is phenylalanine diagnosed?

How is phenylketonuria diagnosed? PKU is diagnosed with a blood test. In the United States and most other countries, a blood test is taken through a heel stick on newborn babies within 48 hours of birth. Further tests will be required to confirm the type of PKU and plan the best way of treating it.

What is a normal phenylalanine level?

The test screens for blood levels of phenylalanine. Normal levels of phenylalanine in the blood are less than 2 milligrams per deciliter (mg/dL). More than 4 mg/dL of phenylalanine in the blood is considered high and may mean your child has PKU.

How do you measure phenylalanine levels?

Blood Phe levels are measured using a small blood sample taken from the heel or big toe of babies and toddlers, and from the fingertip of children and adults. The procedure is easy to manage once you have had a little practice. Your PKU team will usually supply special filter papers needed for the sample.

What effect does phenylalanine have on the body?

Your body needs phenylalanine and other amino acids to make proteins, which are found in your brain, blood, muscles, internal organs, and virtually everywhere else in your body. Phenylalanine is also crucial for the production of other molecules, including (2): Tyrosine.

How do you detect the presence of phenylalanine in a test solution?

Xanthoproteic test is used to detect amino acids containing an aromatic nucleus (tyrosine, tryptophan and phenylalanine) in a protein solution which gives yellow color nitro derivatives on heating with conc. HNO3. The aromatic benzene ring undergoes nitration to give yellow colored product.

What does positive PKU test mean?

Positive phenylketonuria (PKU) test: The test looks for phenylalanine levels in the blood, which should be less than 2 mg/dL. A blood phenylalanine level of more than 4 mg/dL is considered excessive and could indicate that the child has PKU.

How accurate is the PKU test?

Although initial PKU screening demonstrates positive results in 1 percent of infants, there is only a 10 percent chance that an infant with an initial positive result has the disorder (false-positive rate of 90 percent). 6 A repeat test must be performed if the initial test is positive. False-negative results are rare.