Everything you need to know about lab fasting tests

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posted on April 18, 2022 | Author DR. JAVEED KAKROO

If you’re not feeling well and your doctor doesn’t know why, he or she may order lab tests to help you better understand what’s going on inside your body. One test they can order is a fasting lab test. Before this blood test, you may be asked to stop eating or drinking for a few hours. Although not all lab tests require it, some tests require fasting to get the most accurate results. Most of the time, this means that you will be asked to stop eating or drinking between eight and 24 hours before your lab test or blood test, depending on the test.

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.

· Excessive urination and thirst.

· Swollen feet and ankles.

· A high blood pressure reading.

· A yellowish tinge to your skin and/or eyes.

· Fatigue and irregular heartbeat.

· Pale skin and leg cramps.

· Non-specific symptoms difficult to diagnose.

If you have symptoms that don’t seem right, call or see your doctor so they can order the appropriate tests.

If I need a fasting blood test, am I allowed to eat or drink anything?

Some tests allow you to have a few sips of water. However, other tests do not even allow water. You should avoid coffee and gum before a fasting lab test because both of these substances affect your digestive system and can alter your test results. You should also avoid alcohol, tobacco, and exercise.

If you are taking medication, continue to take it as normal unless your doctor tells you otherwise. If you take vitamin/mineral supplements, ask your doctor if you should continue to take them.

Why should I fast?

Foods and drinks can affect your results because sugar, fats, enzymes, minerals and cholesterol are all absorbed into your bloodstream. Affected results could then lead to an inaccurate diagnosis. Here are some conditions you may be tested for that may require a fasting lab test:

· Anemia (iron blood test).

· Diabetes (blood sugar test).

· Electrolyte disorder (metabolic test).

· High cholesterol (blood cholesterol test or lipid profile).

· Kidney function (kidney function panel).

· Liver disease (gamma-glutamyltransferase test).

· Vitamin B12 levels.

What happens if I don’t fast before a blood test?

If you do not fast before a test that requires it, the results may not be accurate. If you forget and eat or drink something, call your doctor or lab and ask if the test can still be done. They can then tell you if you need to reschedule your test.

It’s important to follow fasting instructions before a lab test because a wrong or inaccurate test can lead to more health problems or missed diagnoses. Be honest with your doctor or lab technician if you ate or drank by mistake.

Don’t wait until the day of your blood test to ask if you should fast because some tests require you to fast for 12 hours or more. Thus, you will want to know if your test requires fasting with enough time to follow the fasting instructions.

When can I eat or drink after my lab test?

Once your blood test is done, you can eat and/or drink anything immediately. In fact, it’s a good idea to bring a snack or drink to your appointment. You can also schedule your blood test for early in the morning to minimize the amount of time you will go without food.

When will I receive the test results?

Most fasting lab results are available to your doctor in about 24 hours. However, some tests may take longer. The lab will provide a report to your doctor, and your doctor will use the report to help you with the next steps in your diagnosis and treatment.

(The author is a Microbiologist and Certified Infection Control Auditor Kidney Hospital Srinagar)

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