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 triglycerides assessment in CHANCES cohorts are displayed in attached Excel file .

Eight cohorts can provide data: EPIC Elderly Umeå, ESTHER, HAPIEE, MORGAM, RES, SENECA, Tromsø, and Zutphen). Repeated measurements are available for EPIC Elderly Umeå, ESTHER, RES, SENECA, Tromsø, and Zutphen. However, Zutphen does not have triglycerides measured at baseline (1985) but from their first recontact (1990) onwards. Also, measurement of triglycerides was within a subsample of the total cohort only (those participants who were willing to participate in the OGTT assessment). Therefore, it may (or may not) be possible to treat recontact 1 as “baseline” with regards to triglycerides. Of the other seven cohorts with data at baseline, all have triglycerides measured in all of their samples, though RES does not have triglycerides measurements for RSI-1 at baseline (cohorts RSII and RSIII only). Measurements began for this cohort from RS1-3 onwards (1997-1999). Also, data is missing for RSI-4 (2002-2004) but further information may still be forthcoming. Nevertheless, the cohorts generally used similar methods for the collection, storage, and analysis of triglycerides. Some differences were reported for ESTHER (donation of blood samples at recontacts was voluntary and response rate was lower than at baseline, and nonfasting samples were used at each of the recontacts only), and Zutphen (see above).

Most cohorts have used fasting samples (e.g. overnight). Exceptions to this are evident for ESTHER (fasting status is not known for a proportion of participants at baseline, but for the majority of participants an overnight fast was standard; nonfasting samples only for recontacts), and Tromsø (nonfasting samples). Although fasting status appears to minimally affect triglycerides (Langsted et al, 2008; Lee et al, 2008; Mora et al, 2008), other studies have shown the importance of using fasting triglycerides for cardiovascular disease risk evaluation, for the calculation of LDL cholesterol concentration, and for the classification of subjects into those with and without metabolic syndrome (Sundvall et al, 2011). However, nonfasting values have also been found to be strongly and significantly associated with future cardiovascular events (Bansal et al, 2007; Nordestrgaad et al, 2007). Additionally, Sundvall et al. derived correction factors whereby insufficiently fasted/postprandial serum triglyceride values could be converted into "corrected" fasting values (Sundvall et al, 2008). However, the majority of previous studies, as outlined previously, have suggested that for most lipids, nonfasting samples are as good as fasting samples in predicting cardiovascular risk.

All cohorts who have provided information have used serum for the measurement of triglycerides, but information is still missing from some cohorts.

As with cholesterol, the delay between collection and analysis has been minimal for most cohorts, with cohorts using either refrigeration (1°C to -10°C) or freezing (-20°C to -80°C) for storage. However, the time from collection to analysis varies from a few hours to a few years (ESTHER). Previous studies have shown significant changes in the fatty acid profile of samples stored at 4°C and −20°C, but storage at −80°C up to 10 years does not seem to significantly influence unthawed serum triglycerides (Matthan, 2010). 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, though some stored at −20°C (RES and Zutphen).

Table 3. Triglycerides

* 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

Bansal S, Buring JE, et al. Fasting compared with nonfasting triglycerides and risk of cardiovascular events in women. JAMA 2007;298:309-316.

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.

Matthan NR, Ip B, Resteghini N, et al. Long-term fatty acid stability in human serum cholesteryl ester, triglyceride, and phospholipid fractions. J Lipid Res. 2010;51:2826-32.

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.

Nordestrgaad BG, Benn M, Schnohr P, et al. Nonfasting triglycerides and risk of myocardial infarction, ischemic heart disease, and death in men and women. JAMA 2007;298:299-308.

Sundvall J, Laatikainen T, Hakala et al. Systematic error of serum triglyceride measurements during three decades and the effect of fasting on serum triglycerides in population studies. Clin Chim Acta. 2008;397:55-9.

Sundvall J, Leiviskä J, Laatikainen T, et al. The use of fasting vs. non-fasting triglyceride concentration for estimating the prevalence of high LDL-cholesterol and metabolic syndrome in population surveys. BMC Med Res Methodol. 2011;11:63.

triglycerides.xls (application/msexcel)