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March 11, 2021

Here’s why some medical tests require fasting

Adult Health Fasting

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Blood tests are a common part of preventive care or in preparation for a procedure. You’ll often be sent to a diagnostic center to have your blood drawn and evaluated before receiving the results of the test from your physician. In some cases, you may be asked to fast for a specific amount of time before the test. While it may seem like a trivial part of the process, fasting plays a significant role in ensuring you receive an accurate result.

The basics of fasting for medical tests

A fast is when you abstain from eating or drinking anything other than water for a prolonged period of time. While there are many reasons for fasting, health providers often ask that patients fast before a medical test to avoid anything being absorbed into the bloodstream that could impact the test results. When fasting is required, your doctor will tell you exactly how long you will need to avoid eating and drinking before the test is performed. Medications are generally safe to continue taking while fasting; however, if you are taking any medications that should be taken with food, be sure to consult your physician before you begin fasting.

How strict do I really need to be?

Adhering to the fasting directions provided by your health provider is vitally important as it will ensure your tests accurately measure the composition of your blood at its base level. Eating and drinking anything besides water before a medical test that requires fasting could inadvertently skew results, leading to a misdiagnosis or incorrect recommendation for treatment. If you find it difficult to not eat or drink for extended periods of time, try to schedule your test in the morning — that way, you’ll be sleeping for a significant portion of your fast.

Which tests do I need to fast for?

A basic metabolic panel is one of the most common blood tests ordered by health providers. This test provides information about your metabolism and is often ordered as part of a regular health examination or to identify a medical condition. Fasting is generally required for eight hours prior to taking this test.

Two other common tests that require fasting are glucose tests and lipid tests. Glucose tests are used to diagnose diabetes. They measure your blood sugar and involve a series of blood draws followed by the drinking of a special liquid that contains glucose. Lipid tests measure triglycerides and cholesterol. They help your physician determine your risk of heart disease by monitoring for high levels of these substances in your blood.

If you’re unsure of whether a test requires you to fast or not, always ask your provider. If you wait until the day of your test to seek clarity on what your tests require, you may end up having to reschedule them for another day.

One of the simplest ways to ensure top-quality care is to provide your doctor with accurate information about your health. Fasting — when directed — before a medical test is a key part of that process.

Information on this site is provided for informational purposes and is not meant to substitute for the advice provided by your own physician or other medical professional. You should not use the information contained herein for diagnosing or treating a health problem or disease, or prescribing any medication. If you have, or suspect that you have, a medical problem, promptly contact your health care provider.

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