Logo of archdischArchives of Disease in ChildhoodVisit this articleSubmit a manuscriptReceive email alertsContact usBMJ
Arch Dis Child. 1998 Feb; 78(2): 122–126.
PMCID: PMC1717471

Does a single plasma phenylalanine predict quality of control in phenylketonuria?


A 1993 MRC working group on phenylketonuria suggested standardising blood phenylalanine measurements by taking blood samples at the same time each day. Since it is not known how representative of a 24 hour period a single phenylalanine concentration is, the aim of this study was to investigate the 24 hour variability of plasma phenylalanine in well controlled children with phenylketonuria. Sixteen subjects, 12 girls and four boys aged 1 to 18 years, had hourly venous blood samples collected for 13 hours between 09.00and 21.00 on one day. Serial skin puncture blood specimens were then collected at 24.00, 03.00, and 06.00 within the same 24 hour period. All food and drink was weighed. The median variation in plasma phenylalanine concentration was 155 µmol/l/day, with a minimum of 80 and a maximum of 280. The highest concentration occurred in the morning between 6.00 and 9.00 in 63% of subjects; the lowest occurred between midday and midnight in 94%. Concentrations < 100 µmol/l occurred in 46% of children below 11 years, three having concentrations < 30 µmol/l for two, six, and seven hours respectively. Three of five subjects had concentrations above the MRC guidelines for 24% of the period studied. Except in two subjects, the blood concentrations did not rise in response to phenylalanine consumption. However, the greater the quantity of protein substitute taken between waking and the 16.00 specimen, the larger the decrease in daytime phenylalanine concentration (r = −0.7030) (p < 0.005). There is therefore wide variability in phenylalanine concentrations in a 24 hour period in children with phenylketonuria which is not reflected in a single observation. Further study is needed to investigate the effects of timing of protein substitute on the stability of phenylalanine concentrations.

Full Text

The Full Text of this article is available as a PDF (110K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • van Spronsen FJ, van Rijn M, van Dijk T, Smit GP, Reijngoud DJ, Berger R, Heymans HS. Plasma phenylalanine and tyrosine responses to different nutritional conditions (fasting/postprandial) in patients with phenylketonuria: effect of sample timing. Pediatrics. 1993 Oct;92(4):570–573. [PubMed]
  • MacDonald A, Rylance G, Hall SK, Asplin D, Booth IW. Factors affecting the variation in plasma phenylalanine in patients with phenylketonuria on diet. Arch Dis Child. 1996 May;74(5):412–417. [PMC free article] [PubMed]
  • Gregory DM, Sovetts D, Clow CL, Scriver CR. Plasma free amino acid values in normal children and adolescents. Metabolism. 1986 Oct;35(10):967–969. [PubMed]
  • Scriver CR, Gregory DM, Sovetts D, Tissenbaum G. Normal plasma free amino acid values in adults: the influence of some common physiological variables. Metabolism. 1985 Sep;34(9):868–873. [PubMed]
  • Scriver CR, Lamm P, Clow CL. Plasma amino acids: screening, quantitation, and interpretation. Am J Clin Nutr. 1971 Jul;24(7):876–890. [PubMed]
  • van Spronsen FJ, van Dijk T, Smit GP, van Rijn M, Reijngoud DJ, Berger R, Heymans HS. Phenylketonuria: plasma phenylalanine responses to different distributions of the daily phenylalanine allowance over the day. Pediatrics. 1996 Jun;97(6 Pt 1):839–844. [PubMed]
  • Devlin JT, Brodsky I, Scrimgeour A, Fuller S, Bier DM. Amino acid metabolism after intense exercise. Am J Physiol. 1990 Feb;258(2 Pt 1):E249–E255. [PubMed]
  • Verkerk PH, van Spronsen FJ, Smit GP, Sengers RC. Impaired prenatal and postnatal growth in Dutch patients with phenylketonuria. The National PKU Steering Committee. Arch Dis Child. 1994 Aug;71(2):114–118. [PMC free article] [PubMed]
  • Krause W, Halminski M, McDonald L, Dembure P, Salvo R, Freides D, Elsas L. Biochemical and neuropsychological effects of elevated plasma phenylalanine in patients with treated phenylketonuria. A model for the study of phenylalanine and brain function in man. J Clin Invest. 1985 Jan;75(1):40–48. [PMC free article] [PubMed]
  • de Sonneville LM, Schmidt E, Michel U, Batzler U. Preliminary neuropsychological test results. Eur J Pediatr. 1990;149 (Suppl 1):S39–S44. [PubMed]

Articles from Archives of Disease in Childhood are provided here courtesy of BMJ Group


Save items

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • Cited in Books
    Cited in Books
    NCBI Bookshelf books that cite the current articles.
  • Compound
    PubChem chemical compound records that cite the current articles. These references are taken from those provided on submitted PubChem chemical substance records. Multiple substance records may contribute to the PubChem compound record.
  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles
  • Substance
    PubChem chemical substance records that cite the current articles. These references are taken from those provided on submitted PubChem chemical substance records.

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...