Question

How is phenylketonuria diagnosed?

Answer

The diagnostic methods for phenylketonuria include newborn screening, urine ferric chloride and 2,4-dinitrophenylhydrazine tests, plasma free amino acids and urine organic acid analysis, urine purine analysis, enzymatic diagnosis, and DNA analysis. During the neonatal period, the Guthrie test or colorimetric quantitative determination of phenylalanine can be performed by collecting blood using a thick filter paper. Additionally, the chemical colorimetric method for phenylpyruvic acid in urine can be used for initial screening in older children. The analysis of amino acids and organic acids in plasma and urine can provide biochemical diagnosis evidence and differentiate from other metabolic defects. Urine purine analysis can be used to distinguish different types of phenylketonuria. Enzymatic diagnosis includes the activity measurement of enzymes such as PAH, DHPR, 6-PTS, GTPCH. Currently, PAH and DHPR defects can be diagnosed by DNA analysis.