Journal of Molecular Neuroscience

, Volume 58, Issue 1, pp 102–108 | Cite as

Serum Phenylalanine, Tyrosine, and their Ratio in Acute Ischemic Stroke: on the Trail of a Biomarker?

  • Heidi OrmstadEmail author
  • Robert Verkerk
  • Leiv Sandvik


Fast diagnosis and appropriate treatment are of utmost importance to improving the outcome in patients with acute ischemic stroke (AIS). A rapid and sensitive blood test for ischemic stroke is required. The aim of this study was to examine the usefulness of phenylalanine (PHE) and tyrosine (TYR) as diagnostic biomarkers in AIS. Serum levels of PHE and TYR, measured using HPLC, and their ratio (PHE/TYR) were compared between 45 patients with AIS and 40 healthy control subjects. The relationship between PHE/TYR and the serum levels of several cytokines were also examined. PHE/TYR was significantly higher in AIS patients than in healthy controls (1.75 vs 1.24, p < 0.001). A receiver operating characteristic (ROC) curve analysis of PHE/TYR in AIS patients relative to healthy controls revealed promising sensitivity and specificity, which at an optimal cutoff of 1.45 were 76 and 85 %, respectively. PHE/TYR was positively correlated with interleukin (IL)-1β (r = 0.37, p = 0.011) and IL-6 (r = 0.33, p = 0.025). This study shows that PHE/TYR is highly elevated in the acute phase of AIS, and that this elevation is coupled to the inflammatory response. The ROC analysis documents the possible value of PHE/TYR as a biomarker for AIS and demonstrates its clinical potential as a blood-based test for AIS.


Acute ischemic stroke Diagnostic biomarker Phenylalanine Tyrosine Inflammation 



The authors are indebted to the various staff members of Vestre Viken Hospital Trust, Buskerud, Drammen, and Oslo University Hospital, Ullevål, Oslo, for important contributions to the study. The presented work stems from the research project “Poststroke Fatigue,” for which Dr. Hesook Suzie Kim is the project director and Drs. Grethe Eilertsen, Anners Lerdal, and Heidi Ormstad are the principal researchers. The project is funded by the Research Council of Norway for the period from 2007 to 2010 (project no. 176503/V10), and Vestre Viken Hospital Trust.


The study was approved by The Regional Committee for Medical Research Ethics in Norway and has therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki. Informed consent was obtained from all patients prior to their inclusion in the study.

Conflict of Interest

The authors declare that they have no competing interests.


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Copyright information

© Springer Science+Business Media New York 2015

Authors and Affiliations

  1. 1.Faculty of Health SciencesBuskerud and Vestfold University CollegeDrammenNorway
  2. 2.Laboratory of Medical BiochemistryUniversity of AntwerpAntwerpBelgium
  3. 3.Section of BiostatisticsOslo University Hospital, UllevålOsloNorway

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