Sixty years of research have demonstrated that high cholesterol is a risk factor for heart disease. More specifically, elevated total or low-density lipoprotein cholesterol levels increase your chances for having a heart attack, while a high level of high-density lipoprotein is protective. To find your cholesterol levels, you have to get a lipid panel, which requires a blood test. While you might assume such tests are standardized and straightforward, there are some factors that could affect the accuracy of your results.
Fasting
The blood for your lipid panel should be collected after you have fasted for eight to 12 hours. Laboratory ranges are based on fasting individuals, so eating a meal before your test can artificially elevate your cholesterol levels. Likewise, a diet that contains more fat than usual, such as a meal you might eat around the holidays, can raise cholesterol levels for as long as two weeks.
Timing the Test
Daily and seasonal variations in cholesterol levels are common. According to Mark Deeg, M.D., Ph.D, in "Lipid Topics," your cholesterol can vary from 3 to 5 percent daily, with higher levels usually in the morning. Seasonal variations can approach 12 percent, with highest cholesterol levels typically during the winter. Seasonal variations may reflect differences in activity and diet.
Posture and Activity
Due to changes in blood flow to various organs, your body position can alter cholesterol levels by as much as 15 percent. Levels are highest when you are standing and lowest when you recline. When you arrive at the lab, sit for at least five minutes before your blood is drawn. Because vigorous activity alters cholesterol levels, you should refrain from exercise for 24 hours before your test.
Smoking
Joseph Piscatella, co-author of "Take a Load Off Your Heart," reports that smoking just before a blood draw can increase your cholesterol level. While he does not mention just how long this effect can last, it is best to avoid smoking for at least four hours before your test.
Pregnancy
During pregnancy, women undergo radical metabolic changes. One of these is a 20 to 35 percent increase in cholesterol levels as pregnancy progresses. If at all possible, pregnant women should not have their lipids checked until three to four months after delivery.
Collection Methods
Fingerstick cholesterol measurements, such as those collected at health fairs, run a few percentage points higher than those obtained from venous collections. But venous blood draws can produce inaccurate results, too. If the tourniquet applied to your arm is left in place for even two minutes before your blood draw, your cholesterol reading can increase by as much as 5 percent. At five minutes, your level can increase by 15 percent. The type of anticoagulant in the tube that is used to collect your blood is also important. Ideally, the tube should have a green top.
References
- "Lipid Topics: Variations in Lipid Values"; Mark Deeg, M.D., Ph.D.; 2006
- "Take a Load Off Your Heart"; Joseph C. Piscatella, Barry A. Franklin, Ph.D.; 2003
