Link to other blood tests

Prepared by: Mark O'Doherty and Maria Hughes, UKCRC Centre of Excellence for Public Health, Queens University Belfast, United Kingdom

Details of collected information about total and HDL cholesterol assessment in CHANCES cohorts are displayed in attached Excel file .

Details of collected information about history of dyslipidemia assessment in CHANCES cohorts are displayed in attached Excel file .

Eleven cohorts can provide data: EPIC Elderly Greece, EPIC Elderly Bilthoven (wiki description indicates that both total and HDL cholesterol have been measured), EPIC Elderly Denmark, EPIC Elderly Umeå, ESTHER, HAPIEE, MORGAM, RES, SENECA, Tromsø, and Zutphen. Repeated measurements are available for EPIC Elderly Bilthoven, EPIC Elderly Umeå, ESTHER, RES, SENECA, Tromsø, and Zutphen. Of these 11 cohorts with data at baseline, all have measured total cholesterol. EPIC Elderly Denmark does not have HDL cholesterol measured, and EPIC Elderly Umeå measured HDL cholesterol in a subsample of participants if their serum cholesterol was > 6.7 mmol/l or serum triglycerides were > 2.3 mmol/l. As for repeated measures, the cohorts tended to use similar methods between their baseline and recontacts for the collection, storage, and analysis of samples. Some differences were reported for ESTHER in that donation of blood samples at recontacts was voluntary and response rate was lower than at baseline; as for RES, RSI-1 had nonfasting samples taken at baseline (1990-1993) but the other two cohorts and the subsequent recontacts for RSI used fasting samples; RSI-2 (1993-1995) also did not have any blood measurements taken, so the first recontact for this cohort is RS1-3 (1997-1999); while for Zutphen, recontact 3 used a different method and laboratory than baseline to determine cholesterol in the samples.

Most cohorts have used fasting samples (e.g. overnight). Exceptions to this are noted for EPIC Elderly Greece (where no specific instructions for fasting were given prior to blood collection, though information on fasting status was recorded and is available), ESTHER (where fasting status is not known for a proportion of participants), Tromsø and Zutphen (both having used nonfasting samples). Studies have shown that lipid profiles change minimally in response to normal food intake (Langsted et al, 2008; Mora et al, 2008), and nonfasting lipid profiles may predict increased risk of cardiovascular events (Langsted et al, 2008). Also, it is claimed by Lee et al. that measurements of lipid biomarkers from a single blood sample are a good representation of the average blood levels of these biomarkers and could be useful tool epidemiological studies (Lee et al, 2008). Therefore, whether or not the participants fasted may have minimal impact on the overall analysis within CHANCES.

The majority of cohorts have used serum for the measurement of cholesterol. EPIC Elderly Greece used plasma, but values were converted into serum values with the use of a curve created for the determination of total cholesterol and HDL cholesterol in plasma/serum pairs (Laboratory Methods Committee of the Lipid Research Clinics Program, 1977). Additionally, an estimated negative bias of 3% due to the use of plasma samples may need to be acknowledged in future analyses (Laboratory Methods Committee of the Lipid Research Clinics Program, 1977). Even though no clinical significance is attributable to serum plasma differences, they may be of importance when cholesterol values from different cohorts are being compared. Additionally, the ratio of total cholesterol and HDL cholesterol is predictive in evaluating cardiac risks, and LDL cholesterol may also be calculated from total and HDL cholesterol using the Friedewald calculation (Friedewald et al, 1972).

For most cohorts the delay between sample collection and storage was minimal, with cohorts subsequently using either refrigeration (1°C to 10°C) or freezing (-20°C to -80°C). However, the time from collection to analysis varies between a few hours and several months or years later (ESTHER). A previous study showed that concentrations of serum total and HDL cholesterol are both time and temperature dependent, with the concentrations being mostly affected at room temperature and least affected at freezer temperature (Ignatius et al, 2009). Hence, if samples are to be stored, freezer temperature is highly preferred, which has been the norm within the cohorts that analysed levels after 48 hours from collection (minimal freeze thaw cycles also preferred).

Table 1. Total cholesterol

* Only the recontact of each cohort was counted that was closest to the baseline measurement with respect to follow up duration. RSI shown for RES but full numbers for the other cohorts (RSII and RSIII) can be found in the excel table.

Table 2. HDL cholesterol

* Only the recontact of each cohort was counted that was closest to the baseline measurement with respect to follow up duration. RSI shown for RES but full numbers for the other cohorts (RSII and RSIII) can be found in the excel table.

References

Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972;18:499-502.

Ignatius MC, Emeka NE, Ebele JI, et al. The Effect of Sample Storage on Total Cholesterol and Hdl-cholesterol Assays. Current Research Journal of Biological Sciences. 2009;1:1-5.

Laboratory Methods Committee of the Lipid Research Clinics Program. Cholesterol and triglyceride concentrations in serum/plasma pairs. Clin Chem. 1977;23:60-3.

Langsted A, Freiberg JJ, Nordestgaard BG. Fasting and nonfasting lipid levels: influence of normal food intake on lipids, lipoproteins, apolipoproteins, and cardiovascular risk prediction. Circulation. 2008;118:2047-56.

Lee SA, Wen W, Xiang YB, et al. Stability and reliability of plasma level of lipid biomarkers and their correlation with dietary fat intake. Dis Markers. 2008;24:73-9.

Mora S, Rifai N, Buring JE, et al. Fasting compared with nonfasting lipids and apolipoproteins for predicting incident cardiovascular events. Circulation. 2008;118:993--1001.

cholesterol.xls (application/msexcel)
History dyslipidaemia.xls (application/vnd.ms-excel)