|MadSci Network: Medicine|
Dear, thank you very much for your question regarding high HDL cholesterol. It is in some ways a sticky question, and a lot of work goes into solving it. First, the "normal values". In their simplest form, reference values represent the range of values in which 95 % of the individuals of a study population are found. If a reference value is constructed in this way , 5% of all people will have "elevated" levels by definition. The difficult part is the selection of the study population. Is it representative of the larger population? Are there systematic differences between different groups in the general population ie have gender differences been adequately addressed etc. In the case of cholesterol, reference values are no longer simply averages +/- deviations in study populations. Take the US, for example: The proportion of very heavy people with high and dangerous cholesterol levels is high there - so if we take an "average" section of the population of the US and measure their cholesterol values to construct a reference value from these measurements, the "normal" range will be placed in a region that might actually be dangerous. Therefore, the reference values as they are currently given also include some concept about what "healthy" (as opposed to "normal") cholesterol values should be. For example, the reference value (taken from the Dept. of Clinical Chemistry of a large German University Hospital) for total cholesterol is given as 130 - 260 mg/dl; in a further qualification, <200 mg/dl is given as "optimal", > 250 mg/dl is marked as being "associated with elevated cardiovascular risk". (LDL: < 150 mg/dl = "ideal", 150 - 175 = "suspicious", >175 = "elevated risk". HDL: >65 mg/dl in men/ >55 in women = "standard risk", <45 (m)/ < 35 (f)= "elevated risk"). The values in other countries, such as the US, should be similar. As you can see, a higher level of HDL cholesterol affords protection from cardiovascular risk. So, yes, you can have a situation where total cholesterol is on the "high" side but this elevation is caused solely by an elevation in HDL - and in that situation, there is no elevated cardiovascular risk, although the "raw" cholesterol data would suggest that there was. This is the reason why an isolated cholesterol determination is not recommended to identify people at elevated cardiovascular risk - without information about the other fractions, it cannot guide clinical practice. To do justice to this situation, other "yardsticks" to assess cardiovascular risk have been developed. On of them is the ratio between total cholesterol and HDL - Depending on the situation (age, other cardiovascular risk factors), values of <6.5 or <5 are recommended. Finally, activities to lower total and LDL cholesterol usually lead to higher HDL levels, both in relative and in absolute terms. So if I had to choose between several "elevated" blood values - A high HDL would definitely be my choice! All the best Jens Peter Bork References:  http://circ.ahajo urnals.org/cgi/content/full/111/5/e89 is a nice nontechnical description of the role of HDL written for patients.  http://jam a.ama-assn.org/cgi/content/full/285/19/2486? ijkey=172ba2c4320c52bfc32041fde5950e5e0a14145b&keytype2=tf_ipsecsha At this URL, you find the current guidelines on Detection, Evaluation and Treatment of Elevated Cholesterol, published in 2001. Very technical and demanding, even to a physician. The text (in the Journal of the American Medical Association) is not free, so you would a library with an online subscription. Alternatively, this free publication:  http://circ.ahajournals.org/cgi/content/full/104/15/1863#R3-097189 has a link to the free full text (although without figures and tables). The guidelines are ref. no. 3, there is „Free Full Text“ link on which to click. The article itself is also interesting, dealing with the question of how family physicians can assess cardiovascular risk in an asymptomatic patient from their office desk. All articles are extensively referenced for further reading. If you want to countercheck what reference values for HDL, LDL, total cholesterol etc. are currently used, a Google search will take care of that.
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