Current guidelines for testing blood lipid levels to assess cardiovascular health recommend that patients fast at least 9 hours before having their blood drawn, to ensure an accurate result. But a study appearing today in the Archives of Internal Medicine suggests that fasting may be unnecessary.
The study, by Christopher Naugler, MD, MSc, and Davinder Sidhu, MD, both of the University of Calgary in Alberta, Canada, examined blood draws for assessing lipid levels among 209 180 people over a 6-month period in 2011. They divided patients into groups that were based on the number of hours (from 1 to 16 hours) the patients had fasted before having their blood drawn and then calculated the average of the lipid levels for all of the patients in each group. The average levels of total cholesterol and high-density lipoprotein cholesterol (HDL-C), elements used for calculating 10-year risk scores for having a heart attack, varied by less than 2% regardless of the time spent fasting. There was greater variation with 2 other lipid measures: average low-density lipoprotein cholesterol (LDL-C) levels varied by less than 10%, and average triglyceride levels differed by less than 20%.
Naugler discussed the team’s findings with news@JAMA.
news@JAMA: What prompted you to do this study?
Dr Naugler: It came about from an operational change that we made in my lab in Calgary. We have a number of phlebotomy clinics, and we were turning quite a few patients away for fasting blood work because they weren’t fasting. So then we thought we’d still do the blood work and tell the physician the levels and hours since fasting. We do 35 000 cholesterol checks a month, and we realized we were accruing a large database to look at fasting time and cholesterol levels.
news@JAMA: You found total cholesterol and HDL-C levels were basically the same regardless of fasting time, but there was greater variation for LDL-C and triglyceride levels. Were you satisfied with your findings with regard to what they mean for assessing cardiovascular risk?
Dr Naugler: Yes, particularly for the HDL cholesterol and total cholesterol numbers. Those are significant because they are used for cardiovascular risk classification scores, the Reynolds Risk Score and Framingham Risk Score. LDL cholesterol and triglycerides varied more, but for screening purposes, they don’t figure into the cardiovascular risk scores.
news@JAMA: With the slightly greater variance among LDL-C and triglyceride levels, what do you recommend to physicians whose patients don’t fast and have numbers that are a bit abnormal?
Dr Naugler: There aren’t guidelines to go along with what we’ve found, so we can’t make firm recommendations. But what we tell our doctors locally is if there’s a situation where there’s a small change in a patient’s cholesterol levels that would change how you are managing them, then maybe have the patient come back and test in a fasting state.
news@JAMA: So is fasting overrated?
Dr Naugler: Most of life is not spent fasting. It’s only when you wake up first thing in the morning that you’ve fasted for any period of time. There are some data coming out suggesting that maybe we should be looking at cholesterol levels during normal times—in other words, not after fasting—and maybe the numbers will be just as good or perhaps superior to help us predict cardiovascular risk.