Overview
Lab tests use blood, urine, stool, saliva, or other samples to check health, monitor conditions, or help guide treatment decisions. Good preparation can make results more accurate and may lower the chance that you need to repeat the test. Preparation instructions are not the same for every test, so it is important to check the details before your appointment.
Who Is Affected
Anyone having a lab test may need to prepare in some way. This includes children, adults, older adults, and pregnant people. People with ongoing health conditions or those taking regular medicines may need extra guidance because some tests can be affected by medicines, supplements, dehydration, or recent illness.
Prevention
You cannot always prevent the need for testing, but you can help prevent inaccurate results. Confirm the date, time, location, and whether you need to fast or avoid certain activities. If you are unsure about food, drinks, medicines, or exercise before the test, contact the clinic or laboratory ahead of time.
Diagnosis and Tests
Preparation depends on the type of test. For blood tests, you may be asked to fast for several hours, drink water, or come at a certain time of day. For urine or stool tests, you may need a clean container and clear instructions on how to collect the sample. Some hormone, imaging-related, or timed tests require very specific preparation, so follow the written directions exactly.
Diet and Lifestyle
If fasting is required, ask whether you can drink plain water and whether gum, coffee, tea, or smoking are allowed, because these may affect some results. Alcohol, heavy exercise, and poor sleep can also change certain test results. Wear clothing that allows easy access to your arm if you are having blood drawn, and try to arrive well hydrated unless you were told to limit fluids.
Living With It
If you feel nervous about needles or blood draws, let the staff know before the test. You can ask to sit or lie down and tell them if you have fainted during past blood tests. If a child is having the test, ask the clinic how to prepare them and whether a parent can stay during sample collection.
When to Seek Medical Care
Contact your healthcare professional or the lab before the test if you are sick, have a fever, are vomiting, are dehydrated, or accidentally ate or drank something when fasting was required. Also ask for advice if you missed a dose of medicine, took an extra dose, or are not sure whether to stop anything before the test. Do not stop prescription medicines unless a healthcare professional specifically tells you to.
Questions to Ask a Healthcare Professional
Useful questions include: Do I need to fast, and for how long? Can I drink water? Should I take my usual medicines, vitamins, or supplements? Do I need to avoid exercise, alcohol, caffeine, or smoking? When and how will I get the results, and what should I do if I cannot follow the preparation instructions exactly?