What blood tests are affected by food?

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Certain blood tests are affected by food; do you know what ones? (Shutterstock)

When it comes to visiting the doctor, blood tests can be an important indicator of your overall health, but if you aren’t careful about what you eat before those samples are drawn your results may come back skewed. Correct blood results are necessary for proper medical diagnosis and treatment–you wouldn’t want to be treated for high blood sugar if there really wasn’t an issue! This is why it is important to know what foods affect blood tests.

Similarly, many employers involved with public safety require annual physicals on their staff. Tractor trailer drivers, for example, are often subject to physicals to ensure they are healthy enough to put in the long hours the truck driving industry requires. The Department of Transportation at the federal level requires commercial drivers to pass a physical, and if any levels tested are not within acceptable limits, the driver’s career could be on the line.

So what blood tests are affected by food?

While there are a number of very specific blood tests which can be affected by what you eat, most of these are related to certain diseases, not the everyday general health tests used in an annual examination. For otherwise healthy individuals, the blood tests you need to be on the lookout for, according to Harvard Health Publications and The National Institutes of Health, include:

  • Fecal occult blood test: This test is examines the amount of blood present in stool to verify the presence of gastrointestinal issues. While fasting completely is not practical when you are trying to obtain a stool sample, there are a number of foods which should be avoided several days prior to the sampling.  Red meat should be avoided as the blood it contains can cause a false negative, and radishes, turnips, cabbage, vitamin C supplements, citrus fruit and cauliflower can all turn a test false positive.
  • Blood sugar test: Eating anything with carbohydrates in it before a blood glucose test will change your blood sugar levels. While this is a natural occurrence, doctors looking for signs of diabetes need to know blood sugar levels while you are fasting. If you have high blood sugar after an 8-hour fast, more tests need to be done to see if you are suffering from a condition like diabetes.
  • Triglyceride levels: According to the Cleveland Clinic, fasting before a triglyceride test is important because the amount of triglycerides in the blood is directly related to the food we eat. In fact, triglycerides are the fats from the foods we eat, so eating before this test will absolutely skew levels in the bloodstream. Triglyceride levels are a good indication of LDL or “bad” cholesterol because the body uses triglycerides to carry cholesterol. High triglyceride levels are generally seen as an indicator of heart disease. Because eating dumps fat from food into the body, this test should be performed on a 12-hour fast.

    Blood tests and health

    Blood tests can be an important indicator of your overall health.

  • Blood iron levels: According to WebMD, the only source of the body’s iron comes from food, and because of this, iron levels will fluctuate throughout the day. This is one of the blood tests affected by food simply because food is where it comes from. Most men can go without taking in iron for several days, women, on the other hand, tend to need it supplemented. Only a test done through fasting can give the levels of iron left in the blood without food.
  • Liver function tests: Another one of the common blood tests affected by food is that associated with liver function. Fasting for this test is important because liver enzymes are closely linked to digestive substances, like bile. Eating prior to this test will cause an increase in bile which can create false positives on tests.

If you require blood work make sure to check with your doctor or the clinic staff about requirements. Not all blood work requires fasting, but you need to be certain one way or another. Individuals who need to eat regularly may not be subject to fasting requirements; make sure you discuss any medical complications with your doctor.

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