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Human biomarkers for measuring vitamin B6 intake and status

Vitamin B6 can be assessed by different methods, as shown in Table 1.

Table 1. Assessment methods for vitamin B6
 Biomarker Analysis typeSample  Benefits Intricacies
B6 vitamers   Direct analysis  plasma  Good single B6 indicator  Slow response to intake
 B6 vitamers   Direct analysis  RBC, WB  Status indicator  
 Urinary B6  Direct analysis  Urine  Reflects dietary intake  
 Functional B6  Indirect analysis   Enzyme activities   Assays may be affected by external factors

RBC: red blood cells; WB: whole blood

Direct analysis of vitamin B6

Direct analysis of B6 vitamers has been described in various matrices (1):


Plasma B6 has been often measured by an apo-tryrosine decarboxylase assay. Chromatographic techniques have been used more recently for all type of blood samples.


Includes the analysis of metabolites such as 4-pyridoxic acid often measured using HPLC.


For details on chromatographic techniques for blood, plasma, erythrocyte and urine, see methods in references (5-8):

5.        Talwar et al. J Chromatogr B 2003;792:333-43.

6.       Meisser Redeuil et al. J Chromatogr A 2015.

7.        Yagi et al. J Nutr Sci Vitaminol 2009;56:157-63.

8.       Sharma & Dakshinamurti. J Chromatogr Biomed Applic 1992;578:45-51.

Functional B6 assessment

Several PLP-dependent enzymatic processes have been used for vitamin B6 assessment (1):


PLP-stimulation of α-EAST and α-EALT has been widely used to assess long-term B6 status


For details on α-EAST and α-EALT activities, see method in reference (9): Sorbi et al. Am J Gastroenterol 1999;94:1018.



Urinary xanthurenic acid, normally a minor tryptophan catabolite increases under vitamin B6 depletion


For details on Tryptophan catabolites, see method in reference (11): Liu et al. Clin Chem 1996;42:397-401.



Homocysteine catabolism is a PLP-dependent process, thus homocysteine in plasma is related to vitamin B6 (and folate and B12)


For details on measuring homocysteine in plasma, see method in reference (10): Oosterink et al. J Chromatogr B 2015;998:106-13.


Quality control and technical assistance


Laboratory accreditation and validation

LabCorp (headquartered in Burlington, North Caroline, USA) is a leading global life science company. Licensure/accreditation documentation may be requested by sending an email to:

This is a paid service, with a wide number of options, e.g. vitamin B6, plasma

ARUP Laboratories: A National Reference Laboratory is a US national clinical and anatomic pathology reference laboratory and a worldwide leader in innovative laboratory research and development. A non-profit enterprise of the University of Utah, ARUP offers an extensive menu of highly complex and unique medical tests.

For accreditation documentation see this page.

E.g. vitamin B6 (pyridoxal 5’-phosphate), serum

For other laboratory accreditation and validation schemes, see the OpeN-Global laboratory accreditation page.

Technical assistance

For questions on vitamin B6 methods or for technical assistance, please contact or write to:

Dr Daniela Hampel, PhD
Project Scientist
USDA/ARS Western Human Nutrition Research Center
Department of Nutrition, University of California Davis

Email: or