Wednesday, November 14, 2012

Fasting lipids study: potential practice-changer?

- Kenny Lin, MD

When I last saw my personal physician for a checkup, she recommended that I undergo screening for lipid disorders, per the guidelines of the U.S. Preventive Services Task Force. Although the office had a phlebotomist on site, my appointment was in the afternoon, and I had already eaten breakfast and lunch. Consequently, she instructed me to make a separate morning appointment to have my blood drawn after an overnight fast. Due to my hectic schedule, several months passed before I finally got around to doing this (fortunately, the results were normal). As family physicians know, many patients who are sent for fasting tests never have those tests done at all.

A recent study published in the Archives of Internal Medicine suggests that there may be little reason for most patients to endure the inconvenience of fasting before lipid testing. The authors analyzed the relationship of fasting duration to variations in cholesterol levels obtained in more than 200,000 patients in and around Calgary (Alberta, Canada). In this population, the time since one's last reported meal had no effect on mean total cholesterol and high-density lipoprotein (HDL) cholesterol levels. Mean low-density lipoprotein (LDL) levels varied by up to 10 percent, while mean trigylceride levels varied by up to 20 percent. The authors and two editorialists conclude that for most purposes in primary care, including global cardiovascular risk assessment and monitoring response to pharmacologic treatment, nonfasting cholesterol measurements are likely to yield equivalent information to measurements from traditional fasting samples.

Rare is the single study in the medical literature that changes usual clinical practice on its own, and for good reason. Consistent evidence from multiple studies is usually needed to verify or refute impressive initial findings. Further, the cross-sectional design of this particular study might have masked unmeasured variables that would have been better controlled for in a randomized clinical trial. That being said, if any single study should be called a practice-changer, I think this one fits the bill. What's your opinion?

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