Friday, November 13, 2009


We are all excited about cholesterol because it is a link to heart disease, and that may cause heart attacks and death. All that is true. However, that link must not be taken as religious truth ( I hope that there are still religious truths out there ), so that we live in " the cholesterol fear ". I would like to begin, by emphasizing that serum cholesterol levels, and in particular, the LDL-C ( low density lipoprotein cholesterol, or otherwise called the bad cholesterol ) levels, are correlated with the chance of developing heart artery disease. I reiterate, high LDL-C levels does not equal heart artery disease. It is correlated ( it is a risk factor ) for developing heart artery disease. It is important to note that 40-50% of people who have heart attacks, have normal cholesterol levels, at the time of their heart attacks. I emphasize this because many who consult me, virtually live in fear of cholesterol. When they are told by their GPs that their last blood cholesterol levels are elevated, they feel that they already have blockages and are going to die. That is simply not true. If your blood cholesterol levels are elevated, you maybe at risk of heart artery disease and you should try and bring it down ( so that you reduce your chances of getting heart artery disease ). That is reasonable. But there is no need to " freak-out ".
The issue I wish to raise today is whether it is necessary to have a 12hour ( or 10hours, as some would prefer), fast before taking your blood for cholesterol estimation. Is that an important pre-requisite. That had been the teaching from the very beginning, when we realised that blood cholesterol levels were related to the possibility of developing heart artery disease. This was firmly established for us in the mid-fifties by the Framingham and MRFIT studies. We rationalised that as food affects blood cholesterol levels, we should fast to try and standardise the levels. That made sense. However, we also know that some patients turn up for checkups, without fasting, and should we ask them to return, we may miss the opportunity of detecting his risk to CAD. Should we take his blood ( non-fasted) anyway, and is it accurate enough for clinical decision making?
The latest issue of the Journal of the American Medical Association carried a 68 years survey of 300,000 thousand patients, over 21 countries ( study was led by the research workers from Cambridge ), and found that there was no significance between fasting cholesterol levels and non-fasting cholesterol levels. There were however some difference in the serum triglyceride levels and therefore the levels of the LDL-cholesterol. This is not difficult to understand, as the LDL-C is a lipoprotein and will have fats ( triglycerides ) bound around it, to allow it t swim in the blood stream. These fats. which are triglycerides are easily affected by the ingestion of food and what types of food at what time. So on the one hand, yes, blood cholesterol levels are not really affected by the state of your stomach, but no, the important risk factor, LDL-C can be affected by the state of your stomach. It is also important to state that in commercial estimation of LDL-C, this LDL-C is a derived index. We do not measure LDL-C itself ( this is possible in the research labs. ), but we calculate it from knowing the cholesterol and triglyceride levels. And this calculation can be affected by the levels of triglycerides and this triglyceride levels could be affected by food.
In short, if you wish to have an accurate cholesterol or lipid profile done, it is better to fast, at least 10hours.
As a compromise, one could always do a spot ( non-fasted ) blood lipid profile,and should it be abnormal, then repeat it, truely fasted. Of course, that means two pricks with the needle, two cost and two test.
In my practice, I would rather have the blood taking in the fasting state, for proper heart artery risk profiling.

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