Back to Operations, tests and procedures. It depends on the type of blood test you're having. The healthcare professional arranging your test will tell you if you need to do anything to prepare for it. You can eat and drink as normal before some blood tests. Most fasting lab results are available for your doctor in about 24 hours. However, some tests may take longer to complete.
The lab will provide a report to your doctor, and your doctor will use the report to help with next steps in your diagnosis and treatment. Learn more about the lab services we offer at Bon Secours. Sign up to receive regularly scheduled updates from us packed with healthy news, tips, research, recipes, and more — right to your inbox! When would I need a fasting lab test? If you have one or more of these symptoms, your doctor may order a fasting lab test.
If I need a fasting blood test, am I allowed to eat or drink anything? Why do I have to fast? When can I eat or drink after my lab test? The only exception is the hour period prior to a blood test.
This can lead to a false sense of security. For instance, glucose and triglyceride levels increase after you eat. As it relates to disease risk, how quickly they come down after you finish a meal is important. Some data suggest that after-meal blood levels of glucose and triglycerides are more accurate predictors of disease risk.
If one fasts hours before a blood draw, triglycerides may appear artificially low compared to where they may be during typical non-fasting periods. This again can create a false sense of security regarding your cardiovascular risk. Some people neglect having their blood tested because they cannot fast for an hour period. The encouraging news is that for many individuals, a more realistic reading may be obtained when blood is drawn hours after a normal meal is consumed.
This article provides a novel rationale for what may become the new optimal time to have your blood drawn. The reason fasting is important in this instance is to provide researchers with consistent data on the compound they are testing amongst a large study group.
From the standpoint of optimizing your health, you are not part of a study group. Your purpose for having blood tests is to identify hidden risk factors that are correctable before you are stricken with illness or sudden death. Some credentialed physicians have concluded that individuals do not need to fast before their blood is drawn. They point to studies showing that cholesterol and LDL levels are not significantly altered in most people based on when their blood is drawn fasting or non-fasting.
Like other types of fats, triglycerides are carried in the bloodstream by lipoproteins. Triglyceride-rich lipoproteins contribute to the build-up of plaque in our arteries atherosclerosis.
The fats we consume in our diet are mainly composed of triglycerides. Therefore, following a fatty meal, blood levels of triglycerides will rise. Postprandial after-meal disorders are characterized by fat and glucose that persists in the bloodstream many hours after eating. Postprandial disorders are major causes of heart disease and stroke. Six hours later, the remnants of your meal should be history. Clearance of fat present in your meal ought to be quick and efficient.
After six hours, high levels of absorbed lipids should not be in your bloodstream. In some people, however, meal remnants lipoproteins persist in the blood many hours later.
The longer they stick around, the more opportunity they have to trigger growth of atherosclerotic plaque. Clinical studies show that postprandial triglyceride-rich lipoproteins like VLDL cholesterol are powerful instigators of coronary plaque, carotid plaque, and aneurysms of the aorta.
Although their presence may not be apparent from a fasting blood sample, elevated increases in postprandial lipoproteins can be a critically important risk factor for vascular disease. The box on the next page describes some of the mechanisms by which high levels of postprandial lipoproteins damage our arteries. If after-meal triglycerides are high, this is an even stronger indicator of greater postprandial lipoproteins. Simply put, the higher your triglycerides, the more likely postprandial lipoproteins are also present, potentially putting you at risk for atherosclerotic disease.
However, fasting triglycerides may not be the best way of assessing your atherosclerotic risk. Here are some mechanisms in which high after-meal fats lipoproteins accelerate atherosclerosis: Postprandial lipoproteins block the artery-relaxing agent known as nitric oxide, while increasing the artery constrictor called endothelin. This induces endothelial dysfunction,12,15 which contributes to the formation of atherosclerotic plaque. People with excessive postprandial after-meal abnormalities experience more rapid arterial plaque growth.
The American Heart Association in recent years concurs with our position. Relying on federal government health guidelines can be analogous to living in the medical Dark Ages. When blood sugar spikes too high after eating and remains elevated, this presents a significant mortality risk factor.
Elevated glucose promotes cardiovascular disease and is associated with an increased risk of dementia, cancer, worse outcomes in cancer patients, and accelerated aging. In women, that figure rose to a startling 5. Dangers of After-Meal Glucose Not Yet Fully Recognized When people take blood tests to measure glucose levels, they are asked to fast for 8 to 12 hours.
Doctors request this fasting period because they want a consistent baseline to measure glucose and lipids in comparison with the general population. The problem with fasting is it can cover up the clinical picture of a person who suffers dangerously high blood sugar many hours following a typical meal. In other words, a person may artificially drop their fasting glucose to a safe range after fasting hours, but in their everyday life, they may never fast for this long.
Thus, a fasting glucose blood test can mask what may be a dangerous postprandial after-meal glucose spike. Even tests that measure long-term glycemic control like hemoglobin A1C HbA1C may not adequately detect these post-meal glucose surges.
This means that many individuals are spending at least part of their day in an acute diabetic state. The impact of these multi-hour glucose surges is just now being understood. To put this in perspective, a study was done where after-meal glucose spikes were impeded using a drug that blocks a digestive enzyme. A study of volunteers age early 60s demonstrated that blood glucose in the high-normal range results in significant brain shrinkage.
This shrinkage occurs in regions of the brain involved in memory and other critical functions. In light of evidence linking high normal blood sugar levels with elevated risks of cardiovascular death, cancer, and brain shrinkage, protective steps to reduce glucose levels are critical. For the rest of us, there are steps we can take before meals to impede deadly glucose surges. What measures you take, however, should begin with a comprehensive blood test panel. Consider not fasting prior to your blood draw.
This will likely enable a more realistic analysis of your underlying disease risks and what can be done to protect your precious health. What about Homocysteine?
As it relates to the majority of tests, whether your blood is drawn in a fasting or non-fasting state has little impact on the results.
This includes sex hormones like DHEA, testosterone, estrogen, and progesterone. Blood cell counts and assessments of liver and kidney function are unlikely to be significantly affected based on when you ate prior to a blood draw. When it comes to homocysteine, however, there may be an advantage to having your blood drawn several hours after you eat as opposed to an overnight fast.
The precursor to homocysteine in the blood is the amino acid methionine. Those who ingest red meat often have sharp spikes in homocysteine blood levels. One study showed that men who consumed large amounts of methionine-rich protein had a steady rise in their homocysteine levels throughout the day, but returned to baseline levels the next morning after an overnight fast.
Numerous studies associate high homocysteine with greater incidence of heart attack64,65 and stroke. A huge overlooked confounding factor is that men who consume a lot of red meat may have elevated homocysteine throughout the day, but it drops to normal the next morning.
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