Most Blood Biomarkers Related to Vitamin Status, One-Carbon Metabolism, and the Kynurenine Pathway Show Adequate Preanalytical Stability and Within-Person Reproducibility to Allow Assessment of Exposure or Nutritional Status in Healthy Women and Cardiovascular Patients

Abstract

Knowledge of stability during sample transportation and changes in biomarker concentrations within person over time are paramount for proper design and interpretation of epidemiologic studies based on a single measurement of biomarker status. Therefore, we investigated stability and intraindividual vs. interindividual variation in blood concentrations of biomarkers related to vitamin status, one-carbon metabolism, and the kynurenine pathway. Whole blood (EDTA and heparin, n = 12) was stored with an icepack for 24 or 48 h, and plasma concentrations of 38 biomarkers were determined. Stability was calculated as change per hour, intraclass correlation coefficient (ICC), and simple Spearman correlation. Within-person reproducibility of biomarkers was expressed as ICC in samples collected 1-2 y apart from 40 postmenopausal women and in samples collected up to 3 y apart from 551 patients with stable angina pectoris. Biomarker stability was similar in EDTA and heparin blood. Most biomarkers were essentially stable, except for choline and total homocysteine (tHcy), which increased markedly. Within-person reproducibility in postmenopausal women was excellent (ICC > 0.75) for cotinine, all-trans retinol, cobalamin, riboflavin, α-tocopherol, Gly, pyridoxal, methylmalonic acid, creatinine, pyridoxal 5'-phosphate, and Ser; was good to fair (ICC of 0.74-0.40) for pyridoxic acid, kynurenine, tHcy, cholecalciferol, flavin mononucleotide, kynurenic acid, xanthurenic acid, 3-hydroxykynurenine, sarcosine, anthranilic acid, cystathionine, homoarginine, 3-hydroxyanthranilic acid, betaine, Arg, folate, total cysteine, dimethylglycine, asymmetric dimethylarginine, neopterin, symmetric dimethylarginine, and Trp; and poor (ICC of 0.39-0.15) for methionine sulfoxide, Met, choline, and trimethyllysine. Similar reproducibilities were observed in patients with coronary heart disease. Thus, most biomarkers investigated were essentially stable in cooled whole blood for up to 48 h and had a sufficient within-person reproducibility to allow one-exposure assessment of biomarker status in epidemiologic studies. The Western Norway B Vitamin Intervention Trial was registered at clinicaltrials.gov as NTC00354081.

Plasma Concentrations and Dietary Intakes of Choline and Betaine in Association With Atrial Fibrillation Risk: Results From 3 Prospective Cohorts With Different Health Profiles

“…However, the risk estimates in NORVIT were in general similar to those observed in HUSK and WECAC, making it less likely that the choline and betaine AF risk associations in NORVIT merely reflected persistent or recurrent AF present at baseline. Moreover, the within‐person reproducibility for neither plasma betaine nor choline is excellent 44, 49. Therefore, the risk associations explored based on baseline samples may be underestimated due to regression dilution bias 50…”

Plasma Cystathionine and Risk of Incident Stroke in Patients With Suspected Stable Angina Pectoris

“…Second, the current study is based on the measurement of blood parameters at only 1 time point, thus preventing assessment of the possible variation of cystathionine during follow‐up. However, the within‐subject reproducibility has been shown to be fair to good for plasma cystathionine,26 which allows 1‐exposure assessment of plasma cystathionine status, with reduced risk of regression dilution bias. Third, we performed multiple subgroup comparisons, and it is possible that the significant interaction between cystathionine and previous atrial fibrillation on stroke occurrence is attributed to chance (type I error).…”

Components of One-carbon Metabolism Other than Folate and Colorectal Cancer Risk

“…27 the main weakness of the study was that only a single baseline blood sample from each participant was analyzed, preventing assessment of longitudinal variability in metabolite status. However, we have previously observed a fair to good withinsubject reproducibility over time for betaine, dimethylglycine, and sarcosine, 42 which minimizes the risk of regression dilution bias for these biomarkers. in contrast, reproducibility is poor for choline and methionine, 42 which may suggest that our findings for choline and methionine could be underestimations of the "true" associations.…”

“…However, we have previously observed a fair to good withinsubject reproducibility over time for betaine, dimethylglycine, and sarcosine, 42 which minimizes the risk of regression dilution bias for these biomarkers. in contrast, reproducibility is poor for choline and methionine, 42 which may suggest that our findings for choline and methionine could be underestimations of the "true" associations. another potential drawback of this study and other similar studies in which associations between candidate risk factors and colorectal cancer are sequentially tested in univariate models is that more complex interactions and joint effects of the studied genetic and environmental factors may not be discovered.…”