Paediatric reference values for total homocysteine, tryptophan, tyrosine and phenylalanine in blood spots.

Determining blood concentrations of the amino acids homocysteine, tryptophan, tyrosine and phenylalanine in children is of value in the clinical practice. Over the past decades, the use of blood spot samples to examine amino acid concentrations is increasing rapidly. In children, the use of blood spot samples is especially of relevance, as this method is much less invasive than venous blood sampling. Currently, no paediatric reference values for amino acids in blood spots are available. The aim of the current study was to establish reference values for blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine in school-age children. Dried blood spots were obtained in a community sample of 104 healthy children, aged 6-12 years old (52% males). Blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were determined by positive electrospray liquid chromatography-tandem mass spectrometry. Parents of participants completed questions regarding demographic characteristics. Our sample consisted of healthy children from various ethnic backgrounds, with varying levels of socioeconomic status, in line with the composition of the Dutch society. Blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were similar in males and females, and independent of age. In conclusion, paediatric reference values for blood spot concentrations of total homocysteine, tryptophan, tyrosine and phenylalanine were established, which could be of use in the clinical practice.