One of the most important factors in determining the accuracy and reliability of your lab test is you, the patient. After all, it is a sample from your body (blood, urine, or some other specimen; see Collecting Samples for Testing) on which the test will be performed. Therefore, it is essential that you do the following to ensure that the results will be useful and interpreted correctly by your health care provider:
- Follow instructions, if there are any, to prepare for the specific test you are having performed.
- Alert the person collecting your sample if you have deviated from the instructions and how.
- Inform your health care provider of any medications (including vitamins and supplements) you are taking. If you are taking certain prescribed medications, such as blood-thinners or seizure medication, you may want to write down the exact time at which you took your dose and when your blood was drawn. This information will be useful if your doctor has any questions about your test results.
Certain behaviors may affect some test results, such as recent or excessive exercise, not taking in enough fluids (dehydration), excessive eating, or recent sexual activity. You may be asked to refrain from some of these activities for certain tests.
It should be noted that many tests require no special preparation. But for those that do, be certain to adhere to the instructions provided. If you are ever unclear about the instructions, be sure to ask the person ordering the test for clarification. If you are not given any instructions, you should ask if there are any special instructions needed to prepare for the test.
To help you remember what you need to do before having a lab test, your provider should give you a written copy of instructions, if there are any. In fact, all laboratories that perform moderate and/or highly complex tests are required by the federal government under the Clinical Laboratory Improvement Amendments (CLIA) to provide patients with such written policies. You also may find information about preparations needed for specific tests on web sites like Lab Tests Online. However, you should always follow your health care provider's instructions, as the procedures for a particular test might vary from one lab to another.
One of the more common types of preparation required for testing is fasting (to go without all or certain foods) for several hours before the test or even overnight. Certain tests may require you to increase or decrease the amount you drink for 10 to 12 hours prior to the test. There may be specific foods and medications you will need to avoid. Or you may be asked not to smoke before the test or even not to drink your favorite herbal tea. If you are collecting the specimen at home (such as urine, stool, or semen), you could be asked to follow certain procedures to transport the specimen from home to the lab.
Examples of some common laboratory tests that require advance preparation include:
- Glucose tolerance, fasting, and two-hour post-prandial blood glucose tests: fasting or eating meals at specific times may be required.
- Serum lipids (triglycerides, cholesterol, etc.): fasting for 9-12 hours is usually required.
- Fecal occult blood test: certain food and/or medication restrictions may be required.
- Cortisol: resting before sample collection may be required and, if a saliva sample is to be collected, it may be necessary to refrain from eating, drinking, or brushing teeth for a period of time prior to the test.
On Lab Tests Online, we provide some information about test preparations you may need to follow before taking certain tests. This information appears on the "At A Glance" tab of our test descriptions as well as on the "Test Sample" tab, in more detail when specific patient preparation is needed. Certain instructions for test preparation may sometimes be elaborated on further on "The Test" tab. However, be sure to check with your provider for specific instructions rather than relying on the information on this or any other web site, as different labs may have varying testing protocols.
Finally, with laboratory testing, like other aspects of medical care, it is crucial that you are open and honest with your health care provider. Just as you should give them your complete personal, medical, and family history, you may need to report deviations from preparation instructions and/or medications that you are taking at the time of testing, including vitamins and supplements, as these can affect the results. You also may be asked about the amount of alcohol you consume or tobacco products you smoke. Providing complete, accurate information will help to ensure the reliability of your test results.