The ratio of phenylalanine to tyrosine, a marker of amino acid metabolism.
The phenylalanine to tyrosine ratio (Phe/Tyr) is a calculated value, not a separate blood test. It compares two amino acids: phenylalanine, an essential amino acid from protein, and tyrosine, which the body normally makes from phenylalanine.
The formula is: phenylalanine ÷ tyrosine, using the units reported by the lab.
The enzyme that converts phenylalanine into tyrosine needs to work properly to keep these two amino acids in balance. When that conversion is impaired, phenylalanine builds up and tyrosine falls, raising the ratio. This makes Phe/Tyr a sensitive marker used in screening for phenylketonuria (PKU) and related disorders.
A high ratio suggests reduced conversion of phenylalanine to tyrosine, as in PKU or in states of metabolic and immune stress. A normal ratio is reassuring.
Aniva reads your result against research-backed ranges, not just the lab's wide normal. The reference shown below is specific to this biomarker.
In healthy adults the ratio is typically below about 1.5 to 2, but exact cutoffs depend on the assay and the laboratory. A clearly raised ratio is used as a screening flag for impaired phenylalanine metabolism. Interpret against the reporting lab's reference values with a clinician.
Both amino acids vary with diet and recent protein intake, so timing affects the result. Phenylalanine can rise in liver disease and inflammation independently of an inherited disorder. The ratio is a screening indicator and any abnormal result needs confirmatory testing.
Read with its components, phenylalanine and tyrosine, and alongside a wider amino acid profile where indicated.
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