Stability of red blood cell membrane fatty acid composition after acute myocardial infarction

Questionnaire-based assessment of dietary intake may be invalidated in case-control studies by biases of recall, reporting or interviewing. Biomarkers, free of such biases, can be useful adjunct measures if they themselves are not affected by the event under investigation. Consequently, we studied the stability of the fatty acid composition of the red blood cell (RBC) membrane during a 1-week period, in 20 patients aged 40-74 years after an acute myocardial infarction (MI). Statistical analysis that accounted for a repeated measures design with missing data was undertaken for five fatty acids: C16:0, C18:1, C18:2, C20:5 and C22:6. All fatty acids showed change over the 7 day period. Individuals tended to maintain their relative ranking over time as reflected by correlations between time points of between 0.85 to 0.90, with the exception of C16:0 in which correlations were lower and inconsistent. Over the first 24 hr from admission all fatty acids except C20:5 showed evidence of a statistically significant change. However over the first 7 hr C18:1, C18:2, C20:5 and C22:6 exhibited stability whereas C16:0 altered. We conclude that the fatty acid composition of the RBC membrane appears to change soon after an acute MI. Consequently, case-control studies may be biased towards positive associations for C16:0 and inverse associations for C18:2 and C20:5, i.e. consistent with conventional predictions. However, if blood samples are drawn within 6 hr of admission, bias in estimation of C18:1, C18:2, C20:5 and C22:6 may be unimportant.