BGS graph, modified for direct-HDL

As you may note from one of my published letters (Effect of HDL measurement Technique on Clinical Lipidology, in the Journal of Clinical Lipoidology, 2008;2(5):401-302), the technology for measuring HDL has changed. The direct method of measuring HDL has replaced the indirect method of measuring HDL. While the newer technique is simpler and hence is more accurate, it does not give the same HDL values as did the older method–indeed, the newer method gives a HDL value about 10 mg/dl (0.25 mmoles/L) higher than the older method, and since we calculate the LDL value–to save money–based on the HDL value, the subsequent LDL value will be 10 mg/dl (0.25 mmoles/L) lower when the newer method is used than when the older method is used. This point is NOT trivial, as my letter shows.

If one only focuses on LDL, then all one has to do is to lower the LDL target by 10 mg/dl. However, focusing solely on LDL either under predicts the population at risk of atherothrombotic disease (ATD) and thus fails to treat people at risk of ATD–or treats people who are not at risk of ATD, at least not at risk of ATD until old age. The accurate prediction of the population at risk of ATD requires the use of HDL. This point is of the utmost significance since virtually all of the studies that we use to determine our goals of treatment were done using the indirect method of HDL determination. Hence ALL of our treatment goals are based on the older technology, with the result that your lab test may look great on paper while cholesterol is building up in your artery walls.

Since a number of the physicians with whom I correspond are not converting the direct method back to the indirect method–why I don’t know–I have decided to modify the BGS graph to the equivalent had the direct method been used all along. To do this I took the CRF-SBP plots of my ATD patients whose plots lay close to the threshold line and converted them from the indirect method to the equivalent direct method results. I then plotted the newer plots on the graph, indicating those CRF-SBP pots originally above the line in red and those CRF-SBP plots originally below the line in green. I then re-drew the threshold line to fit between the red and green plots. This modified threshold line has the co-ordinates (0.62,100) and (0.40,140). This line fits fairly well. Only one patient ( a 79 year old man) is misclassified on the modified graph–he was originally above the line, but is now below the modified threshold line. Now everyone can use the BGS graph.

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