Phenylalanine

Phenylalanine too high

A slightly raised value is usually caused by a protein-rich meal or a lot of products containing aspartame shortly before the sample collection. Liver disease and serious illness or infection can also raise phenylalanine. A slightly raised value does not cause symptoms by itself. Rarely, a strongly raised value fits PKU or a milder form of it; in adults, PKU is almost always already known from the heel prick.

Phenylalanine too low

A low value is often caused by fasting, a low-protein meal, strenuous exercise or normal fluctuations during the day. Eating little or little protein for a long time, malnutrition, serious illness and pregnancy can lower several amino acids at once. A low value of one amino acid does not mean you need that amino acid as a supplement. Rarely, a low value fits an inborn disorder in the production of an amino acid.

Useful for

In hospitals, a specialist uses this test when a metabolic disorder is specifically suspected, or to monitor a known metabolic disease and the diet that goes with it. For adults without symptoms, to find nutritional deficiencies or to choose supplements, the test is not useful according to current knowledge. If you use protein supplements or single amino acids, you get a result that mainly shows that intake.

How common is it?

Inborn disorders of amino acid metabolism are rare. In the Netherlands, the heel prick finds on average about 12 children with PKU (phenylketonuria) per year and about 1 child with MSUD (maple syrup urine disease) or tyrosinemia type 1. There are no Dutch figures on abnormal amino acid values in adults without symptoms.

RIVM, heel prick screening (pns.nl)