Wednesday, September 16, 2009

Do I have to fast before my blood tests?

Do I have to fast before my blood tests?

It's almost always necessary to fast before a blood cholesterol test. If you're scheduled for a blood cholesterol test, you'll want to make sure you're fasting properly. Both your doctor and the lab where you'll have your blood work drawn are 2 good resources to help you determine how to fast before a blood cholesterol test.
You do not have to fast unless your doctor has ordered a fasting glucose, fasting lipid panel, fasting metobolic panel, fasting cholesterol, HDL or tryglyceride.
Fasting Dos and Don'ts
Stay hydrated and drink plenty of water. Take any medication that your doctor prescribed to you except for corticosteroids, estrogen or androgens, oral contraceptives, some diuretics, anti-psychotic medications including haloperidol, some antibiotics and niacin.

Do not smoke, drink any other liquid than water or exercise during your fast. Even chewing gum is off limits. Any of these elements can adversely affect your test results.


How to Fast Before a Blood Cholesterol Test

It's almost always necessary to fast before a blood cholesterol test. If you're scheduled for a blood cholesterol test, you'll want to make sure you're fasting properly. Both your doctor and the lab where you'll have your blood work drawn are 2 good resources to help you determine how to fast before a blood cholesterol test.

How long should I fast?
If your doctor did not tell you how long to fast, you should not eat or drink anything for approximately 12 hours prior to the test. Fasting means you should not eat or drink any liquids except for water.

Fast for eight hours before a glucose tests. The test is typically conducted in the morning while your body is still in a resting place for a more accurate reading.

You must fast at least 12 hours before taking a cholesterol blood test to get an accurate reading on triglycerides. The American Heart Association warns against quick cholesterol tests you find in malls and health fairs because fasting is imperative to obtaining an accurate result. http://www.ehow.com/way_5332776_long-fast-before-blood-test.html

Instructions
  1. Step 1

    Check with your doctor or the lab where you'll be having blood drawn to find out how long you're required to fast. Sometimes this time frame is 6 to 8 hours and sometimes you might have to fast overnight. In some cases, you'll have to fast for up to 12 hours.

  2. Step 2

    Schedule your blood cholesterol test as early in the morning as possible if you're required to fast for 12 hours. You can stop eating at 6 p.m. or 7 p.m. And then wake up the next morning and go right to the lab to have your blood drawn.

  3. Step 3

    Pay attention to what you're eating in the weeks prior to a blood cholesterol test, assuming you have that much advance notice that you'll be getting this test. Avoid red meat, eggs and other high-fat and high-cholesterol foods if you're getting a blood cholesterol test as part of a life insurance exam.

  4. Step 4

    Don't alter your diet too much if you're getting a routine blood cholesterol test since your doctor will want an accurate idea of what your cholesterol is based on your usual diet.

  5. Step 5

    Drink water even after your fast has begun. Most lab facilities still allow patients to drink water and don't consider what to be part of the fast, no matter how many hours you're required to fast.

  6. Step 6

    Check with your doctor or the lab to determine if coffee is allowed. In some cases, you're not required to avoid coffee when you're fasting.

  7. Step 7

    Be honest when you go for your blood cholesterol test. If you were required to fast for 12 hours, and you only fasted for 8 hours because you had a snack before bedtime, let the lab know.


Why is it important to fast before a blood test?

That depends on what your doctor is trying to test! There's ways to test your cholesterol without fasting before a blood test - but unfortunately, the results won't be as accurate. Doctors may also order a blood test to check your glucose levels instead, and again there are versions of the test which don't require fasting, while others do.

If your cholesterol has tested high in the past, your doctor will want to monitor your cholesterol levels. This is especially important if you're taking a cholesterol medication - or if your family history places you at higher risk for heart disease. Unfortunately, there's several different kinds of cholesterol - good cholesterol (HDL), bad cholesterol (LDL) and very-low-density-lipoprotein (VLDL). And some cholesterol tests will be affected dramatically by what you've eaten before the test.

The measure of your total cholesterol isn't affected as much by your recent meals, according to
Harvard Health Publications - and some versions of this test can even be performed at home! But doctors prefer to get a more detailed picture, which is why they perform tests which screen for all the components of your total cholesterol count. But even these tests don't measure your bad cholesterol directly. It's calculated by subtracting the good cholesterol and triglycerides from your total cholesterol level. Whatever's left is your bad cholesterol level!

And after a meal, your triglyceride level increases 20 to 30 percent, according to Harvard. So the extra triglycerides in your bloodstream would also get subtracted from the total cholesterol score - which would make bad cholesterol levels seem lower than they actually are. (And fasting isn't the only thing that affects the calculation. Psychological stress affects your HDL levels - and so does infection or injury!)

Blood tests are also ordered for diabetic patients, or to screen for diabetes. But in these cases, the doctor isn't testing the blood's cholesterol levels. Instead, a glucose test measures the amount of sugar in the bloodstream, to determine how the body is processing carbohydrates. The
National Institute of Health notes that there's two kinds of glucose test, and only one of them requires fasting. A random glucose test can be performed at any time of day - even after a meal. But if the doctor wants to check your blood sugar levels after fasting, then you'll have to avoid eating before the test!

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1 comment:

Ryan said...

I don't think fasting is necessary to have cholesterol tests. But the doctor should be consulted first.

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