You’re sitting in the waiting room, wondering if the gurgles and growls coming from your stomach after your overnight fast are really as loud as you think they are, as you politely yet awkwardly avoid eye contact with other patients.
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If you’ve had your blood drawn for a lipid profile to check the levels of different types of cholesterol in your body, you know the drill: You fast for 12 hours, drinking only water, and you get the earliest appointment you can in the morning so that you can grab some caloric fuel and caffeine as soon as the test is over.
While it’s still not advisable for most patients to order a side of breakfast with their next lipid test, the results of a recent large-scale study have challenged conventional thinking about that ubiquitous pre-lipid test fast. The analysis found that fasting times don’t have nearly as much of an impact on certain cholesterol levels as once believed.
“Presuming the study results are correct—and with greater than 200,000 patients it was exceedingly powerful—it will change our paradigm to a significant degree, especially as related to certain patients with diabetes or other conditions where fasting could be particularly harmful,” says Cleveland Clinic cardiologist Curtis Rimmerman, MD, MBA.
Average levels for fasting and nonfasting patients varied as follows:
- Total cholesterol—2 percent
- High Density Lipoprotein (HDL) or “good cholesterol”—2 percent
- Low Density Lipoprotein (LDL) or “bad cholesterol”—10 percent
- Triglycerides—20 percent.
“Frankly, the differences don’t matter as it pertains to total cholesterol and HDL cholesterol, because there was only a 2 percent difference, and that could just be a lab variation or a variation from one day to another,” Dr. Rimmerman says. However, the variations in LDL cholesterol and triglyceride levels hold greater clinical significance and support the case for fasting before lipid testing for the majority of patients to obtain the most accurate panel possible for routine checkups, he says.
Interestingly, an important marker of cardiovascular health that cardiologists are relying on more and more—non-HDL cholesterol—likely would not be affected by fasting. The measure is calculated by subtracting your HDL from your total cholesterol. “If there’s only a 2 percent variation between patients who fast and don’t fast for total cholesterol and HDL cholesterol, then the non-HDL cholesterol calculation isn’t significantly affected,” Dr. Rimmerman points out.
For now, Dr. Rimmerman says that he will continue to adhere to a fasting regimen for most patients because the practice provides the most accurate test possible, especially when making comparisons to past blood tests.
In certain situations, however, the results of the study offer valuable clinical applications. “Whereas we used to reschedule a blood test if a patient was not fasting, we could go ahead with it now that we have this information,” Dr. Rimmerman says. For those patients with diabetes or other conditions for whom fasting can be risky, he says: “Now we can tell them not to fast and can still rely on the numbers.”
Lipid blood tests