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 may be used to:

• Help diagnose or screen for a specific disease or condition. Screening helps diagnose diseases before you have any symptoms.
• Monitor a disease or see if treatment is working.
• Give you more general information about your organs and body systems. Lab tests may be ordered with your annual checkup or preventative testing.

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

• Following all the instructions given to you by your 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 glucose (blood sugar) levels. Taking the medicines too close to a blood glucose test could change your results.
• Telling your provider about any medicines, vitamins, or supplements that you are taking.

Taking these steps can help make sure that 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 to 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 your bloodstream. These nutrients might still be in your bloodstream when you have your test and may change the results of certain blood tests. Fasting can help to improve the accuracy of your test results. The length of time you need to fast 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 may 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. But don't stop taking any medicines unless your provider tells you to.

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:

• Blood Glucose Test
• Cholesterol Levels Test
• Triglycerides Test
• Calcitonin Test

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 period of time 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 various foods. These may 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?

Talk to your provider if you have questions or concerns about test preparations. They will let you know if there are any special instructions to follow.

Be sure you understand your preparation instructions before the day of your test.