Method(s): LC-MS/MS (1).
What is creatine?
Creatine plays an essential role in energy storage and transmission. It is synthesized by arginine:glycine amidinotransferase, which forms guanidinoacetate, which in turn undergoes methylation, catalyzed by S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase, forming creatine. Creatine in plasma/serum is a biochemical marker of primary and secondary creatine defects. The reason for the inclusion of creatine into the analytical repertoire of BEVITAL is a marked decrease in plasma level (up to 40 %) in vitamin B6-deficient subjects (2).
Performance of the assay
Lower limit of detection (LOD): 1 µmol/L.
Within-day CV: 2.3-2.9 %; between-day CV:2.7-3.2 %.
Detection of primary and secondary creatine defects. Assessment of vitamin B6 status?
Specimen, collection and processing
Patient/subject: Creatine concentration is increased in subjects taking creatine supplements.
Matrix: EDTA plasma and serum.
Volume: Minimum volume is 50 µL, but 200 µL is optimal and allows reanalysis.
Preparation: 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: Creatine in plasma/serum decreases with age, as described in a recent article. Median (2.5th -97.5th percentile) is 60 (16-97) µmol/L at the age of 0-12 years, 48 (14-92) at the age of 13-20 years and 31 (13-57) at the age > 20 years.
Intraclass correlation coefficient (ICC):
1. Midttun, O., Kvalheim, G., and Ueland, P.M. (2013). High-throughput, low-volume, multianalyte quantification of plasma metabolites related to one-carbon metabolism using HPLC-MS/MS. Anal Bioanal Chem 405, 2009-017.
2. da Silva, V.R., Rios-Avila, L., Lamers, Y., Ralat, M.A., Midttun, O., Quinlivan, E.P., Garrett, T.J., Coats, B., Shankar, M.N., et al. (2013). Metabolite profile analysis reveals functional effects of 28-day vitamin B-6 restriction on one-carbon metabolism and tryptophan catabolic pathways in healthy men and women. J Nutr 143, 1719-727.