PAr index

Method(s): LC-MS/MS (1).

What is measured on the same platform, click here.
Platform D: PLP, PL, PA, (PAr), PN, Thi, TMP, Ribo, FMN, Cysta, Neopt, Trp, Kyn, (KTR), KA, AA, HK, XA, (HK/XA), HAA, Pic, QA, NA, NAM, mNAM, Cot, OHCot, Trig

What is the PAr index?

PAr index is the ratio of 4-pyridoxic acid divided by the sum of pyridoxal 5´-phosphate plus pyridoxal (PA/(PLP+PL)). Inflammatory markers account for more than 90 % of the explained variance of PAr, which efficiently discriminates subjects with high inflammatory status. It is only slightly influenced by vitamin B6 intake and reflects increased vitamin B6 catabolism during inflammation (2, 3).

Performance of the assay (LC-MS/MS)

Lower limit of detection (LOD) (PA/PLP/PL): 0.5/ 0.2/ 0.2 nmol/L.
Within-day CV: na; between-day CV: na.


Assessment of vitamin B6 catabolism during inflammation. PAr should be regarded as a marker of inflammation.

Specimen, collection and processing

Patient/subject: PAr is essentially not influenced by vitamin B6 intake, and only moderately affected by supplementation with high doses of pyridoxine.
Matrix: EDTA plasma and serum.
Volume: Minimum volume is 60 µL, but 200 µL is optimal and allows reanalysis.
Preparation and stability: See separate B6 vitamers. The PAr index is essentially not influenced by the conversion of PLP to PL that occurs during non-optimal handling of serum samples. The blood sample must be centrifuged and the plasma/serum fraction put on ice, and frozen.

Transportation; for general instruction on transportation, click here.

Frozen, on dry ice.

Reported values, interpretation

Reported values: 0.29-0.51.
Intraclass correlation coefficients (ICC): 0.75.


1. Midttun, O., Hustad, S., and Ueland, P.M. (2009). Quantitative profiling of biomarkers related to B-vitamin status, tryptophan metabolism and inflammation in human plasma by liquid chromatography/tandem mass spectrometry. Rapid Commun Mass Sp 23, 1371-79.
2. Ulvik, A., Midttun, O., Pedersen, E.R., Eussen, S.J., Nygård, O., and Ueland, P.M. (2014). Evidence for increased catabolism of vitamin B-6 during systemic inflammation. Am J Clin Nutr 100, 250-55.
3. Ueland, P. M., A. McCann, O. Midttun and A. Ulvik (2017) Inflammation, vitamin B6 and related pathways. Mol Aspects Med 53:10-27.