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How to Prepare for a Lab Test

How do I prepare for a lab test?

A laboratory (lab) test is a procedure in which a health care provider takes a sample of your blood, urine, other body fluid, or body tissue to get information about your health. Lab tests are often used to help diagnose or screen for a specific disease or condition. Screening helps diagnose diseases before symptoms occur. Other tests are used to monitor a disease or see if treatment is effective. Lab tests may also be done to provide more general information about your organs and body systems.

For any type of lab test, you should prepare for it by:

  • Following all the instructions given to you by your health care provider
  • Telling your provider or lab professional if you didn't follow these instructions exactly. It's important to be honest. Even a minor change from the instructions can have a big effect on your results. For example, some medicines raise or lower blood sugar levels. Taking them too close to a blood sugar test could affect your results.
  • Telling your provider about any medicines, vitamins, or supplements that you are taking

Taking these steps can help ensure your results will be accurate and reliable.

Will I need to take other steps to prepare for my lab test?

For many lab tests, you don't need to do anything other than answer questions from your provider and/or lab professional. But for others, you may need do some specific preparations before the test.

One of the most common lab test preparations is fasting. Fasting means you should not eat or drink anything except water for up to several hours or overnight before your test. This is done because nutrients and ingredients in food are absorbed in the bloodstream. This can affect certain blood test results. The length of fasting can vary. So if you do need to fast, make sure you ask your provider how long you should do it.

Other common test preparations include:

  • Avoiding specific foods and drinks such as cooked meats, herbal tea, or alcohol
  • Making sure not to overeat the day before a test
  • Not smoking
  • Avoiding specific behaviors such as strenuous exercise or sexual activity
  • Avoiding certain medicines and/or supplements. Be sure to talk to your provider about what you are currently taking, including over-the-counter medicines, vitamins, and supplements.

For some blood tests, you may be asked to drink extra water to help keep more fluid in your veins. You may also be asked to drink water 15 to 20 minutes before certain urine tests.

What types of lab tests require special preparation?

Some of the most common lab tests that require fasting include:

Some of the most common lab tests that require other special preparations include:

  • Creatinine Test, which may require fasting or avoiding cooked meats
  • Cortisol Test. For this test, you may need to rest for a bit before your sample is taken. You may also have to avoid eating, drinking, or brushing your teeth for a certain time period before your test.
  • Fecal Occult Blood Test. For this test, you may need to avoid certain foods or medicines.
  • 5-HIAA Test. For this test, you may be asked to avoid a variety of specific foods. These include avocados, bananas, pineapples, walnuts, and eggplants.
  • Pap Smear. A woman may be instructed not to douche, use tampons, or have sex for 24 to 48 hours before this test.

Is there anything else I should know about preparing for a lab test?

If you have questions or concerns about test preparations, talk to your health care provider. Be sure you understand your preparation instructions before the day of your test.


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The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.