Assessment of reproducibility and biological variability of fasting and postprandial plasma metabolite concentrations using 1H NMR spectroscopy.

INTRODUCTION: It is crucial to understand the factors that introduce variability before applying metabolomics to clinical and biomarker research. OBJECTIVES: We quantified technical and biological variability of both fasting and postprandial metabolite concentrations measured using 1H NMR spectroscopy in plasma samples. METHODS: In the Netherlands Epidemiology of Obesity study (n = 6,671), 148 metabolite concentrations (101 metabolites belonging to lipoprotein subclasses) were measured under fasting and postprandial states (150 minutes after a mixed liquid meal). Technical variability was evaluated among 265 fasting and 851 postprandial samples, with the identical blood plasma sample being measured twice by the same laboratory protocol. Biological reproducibility was assessed by measuring 165 individuals twice across time for evaluation of short- (<6 months) and long-term (>3 years) biological variability. Intra-class coefficients (ICCs) were used to assess variability. The ICCs of the fasting metabolites were compared with the postprandial metabolites using two-sided paired Wilcoxon test separately for short- and long-term measurements. RESULTS: Both fasting and postprandial metabolite concentrations showed high technical reproducibility using 1H NMR spectroscopy (median ICC = 0.99). Postprandial metabolite concentrations revealed slightly higher ICC scores than fasting ones in short-term repeat measures (median ICC in postprandial and fasting metabolite concentrations 0.72 versus 0.67, Wilcoxon p-value = 8.0×10-14). Variability did not increase further in a long-term repeat measure, with median ICC in postprandial of 0.64 and in fasting metabolite concentrations 0.66. CONCLUSION: Technical reproducibility is excellent. Biological reproducibility of postprandial metabolite concentrations showed a less or equal variability than fasting metabolite concentrations over time.

Overweight can be used as a tool to guide case-finding for cardiovascular risk assessment.

BACKGROUND: In general practice, it is too time-consuming to invite all patients for cardiovascular risk assessment. OBJECTIVE: To examine how many patients with an indication for treatment with cardiovascular medication can be identified by ad hoc case-finding when all patients with overweight/obesity are invited for risk assessment. METHODS: A cross-sectional analysis of the baseline measurements of the Netherlands Epidemiology of Obesity study, a population-based prospective cohort study in 6673 persons aged 45-65 years. We calculated the proportion of participants with a treatment indication using the risk prediction Systematic COronary Risk Evaluation (SCORE-NL 2011), for lean, overweight and obese participants. Participants with a history of cardiovascular disease, diabetes mellitus or rheumatoid arthritis or using cardiovascular medication were not eligible for ad hoc case-finding because they were already identified as being at risk and/or had been treated. RESULTS: Of the study population, 30% had already been identified and/or treated with cardiovascular medication and were therefore not eligible for ad hoc case-finding. Of the eligible participants, 47% were lean, 41% overweight and 12% obese. Of the participants with overweight, 12% had a treatment indication and of the participants with obesity, 19% had a treatment indication. Of all participants with a treatment indication 24% were not yet treated. Of all participants with a new treatment indication, 70% had overweight or obesity. CONCLUSIONS: Of the participants with a treatment indication, 24% were not yet treated. Inviting patients with overweight/obesity for cardiovascular risk assessment may help to detect 70% of these residual patients with a treatment indication.

Cardiovascular risk assessment in haemophilia patients.

Haemophilia patients have a reduced cardiovascular mortality, which may be the result of a lifelong deficiency of factor VIII or IX. On the other hand, the prevalence of risk factors may differ in these chronically ill patients compared to the general population. The prevalence of risk factors and expected risk of cardiovascular disease was compared in haemophilia patients and healthy controls. In adult haemophilia A and B patients, body mass index, blood pressure, cholesterol levels and fasting glucose levels were measured and compared to healthy age-matched males. The expected risk of mortality due to cardiovascular disease was calculated using a European risk prediction algorithm (SCORE). A total of 100 haemophilia A and B patients and 200 healthy controls were analysed. The mean age of the patients was 47 years (range 18-83). The number of haemophiliacs with hyperglycaemia (24%) and hypertension (51%) was higher than in the controls (p-values 0.001 and 0.03, respectively). The mean low-density lipoprotein (LDL) cholesterol level in cases was lower than the controls (3.02 mM (0.69-6.57) and 3.60 mM (1.68-5.95), respectively, p < 0.001). Fewer cases had increased LDL levels (p=0.045). No difference was found in the 10-year cardiovascular mortality risk >10% between cases and controls (12% and 7%, respectively, p = 0.18). The prevalence of risk factors and expected risk of cardiovascular disease in haemophilia patients is comparable to the general population. This strengthens the hypothesis that hypocoagulability may reduce cardiovascular mortality in haemophilia patients.

No added value of the methionine loading task in assessment for venous thrombosis and cardiovascular disease risk.

Homocysteine is a risk factor for cardiovascular disease and venous thrombosis. Clinical guidelines differ in their recommendation whether or not to measure homocysteine after methionine loading. In this study, we investigated the added value of the methionine loading test next to fasting homocysteine levels for identifying subjects at risk for venous thrombosis or cardiovascular disease, using Receiver Operating Characteristic (ROC) curves. The analysis was performed in 185 patients with recurrent venous thrombosis, 130 patients with cardiovascular disease and 601 controls. The discriminatory power of the fasting homocysteine measurement alone for identifying subjects at risk of venous thrombosis expressed as the area under the ROC curve (AUC) was 0.61 (95%CI 0.56-0.66). Using both a fasting homocysteine measurement and a methionine loading test together yielded a similar AUC of 0.65 (95%CI 0.60-0.69), indicating no added value of methionine loading next to fasting homocysteine measurement in identifying subjects at risk for thrombosis. Similar results where found for cardiovascular disease,with an AUC of 0.62 (95%CI 0.57-0.67) for the fasting homocysteine measurement alone and an AUC of 0.62 (95% CI0.57-0.67) for the combination of both the fasting and the post-load homocysteine measurement. The methionine loading test has no added value next to measuring fasting homocysteine levels for identifying subjects at risk for venous thrombosis or cardiovascular disease and for that reason should not be used in clinical practice.

Impact of serological methodology on assessment of the link between Chlamydia pneumoniae and vascular diseases.

We assessed the impact of five serologic tests on the link between Chlamydia pneumoniae and abdominal aortic aneurysms (AAA). The results of the tests were inconsistent. Agreement among the five tests was generally poor. Detection of the link between C. pneumoniae and AAA depends on the serologic methodology chosen.