Why Do You Need to Fast Prior To A Blood Test?

Why Fast Prior To A Blood Test? 

Blood tests are conducted for diagnosing, monitoring, and screening various medical conditions. It involves the diagnostic testing of a blood sample in a laboratory. The lab technician will draw blood through venipuncture. While most lab tests don’t require fasting, some do need you to go without food for a certain period of time. So, why do you need to fast prior to a blood test? At Family Doctors Medical Center, we would like to answer this question and provide you with relevant helpful insights. 

Why Fasting is Essential Before Certain Blood Tests? 

There is an important reason why your medical doctor will require you to fast before your blood test. It will help improve the accuracy and reliability of the test. Proper and accurate test results are important for diagnosing different health conditions and monitoring the effectiveness of the treatments. Food and drinks contain nutrients that can enter your bloodstream and interfere with your blood results. 

When you take food, it contains a variety of nutrients, including carbohydrates, vitamins, minerals, proteins, and fats. These nutrients are broken down and get absorbed into the bloodstream. This will certainly affect the levels of different substances in your blood and affect the lab test results. 

The different substances that get absorbed into the bloodstream and affect the test results include: 

  • Sugar 
  • Enzymes 
  • Fats 
  • Cholesterol 
  • Minerals 

Such results could then create an inaccurate diagnosis, further affecting the effectiveness of the treatment plan. Consider the following example. Your doctor requires you to undergo certain diabetes testing to measure your baseline blood sugar levels after fasting for a certain period of time. If you eat something right before your tests, it will cause your blood sugar levels to spike, thus rendering your test results to be inaccurate. This can result in misdiagnosis as prediabetes or diabetes.  

What Happens If You Don’t Fast? 

As mentioned above, if you don’t fast before your blood test, the results can be inaccurate. If you forget the need to fast and take something, it is recommended to call your lab or doctor and ask whether the test can still be performed. They will then inform you whether to reschedule the test or not. 

It is important to be honest with your lab technician if you took anything by mistake. An inaccurate test can not only cause missed diagnoses but can also create more health issues. Certain lab tests can require you to fast for 12 hours or even more.  

If you don’t inform your doctor or lab technician, it is likely they may interpret your non-fasted test results. In that case, they will require you to reschedule the blood test at a different time when you are able to complete your fast before the test. 

Can You Drink Water Before Your Blood Test? 

You can drink water while fasting for your blood test. Taking plenty of water can, in fact, help improve the chances of more accurate test results. Avoid getting dehydrated because it can adversely affect some types of blood tests, including: 

  • Electrolyte test 
  • Cholesterol test 
  • BUN test 

Make sure to maintain hydration before your test by taking the right amount of water for your body weight and activity levels. It is best to ask your medical doctor about this. 

Eating or Drinking After Your Lab Test 

Once the technician has drawn your blood, you can eat or drink anything. Bring a snack/drink to your lab appointment. Schedule such blood tests in the early morning, as it helps minimize the duration of time you will have to go without food. 

Can You Take Your Medication Before Blood Tests? 

If you take any prescribed medications, take them with water as usual. You should let your doctor know about this so that they can instruct you properly. However, supplements and vitamins are an exception here. They affect lab results, so avoid taking them before taking your tests.

It is not just food and drinks that you need to be concerned about when fasting before your blood test. You should also avoid anything that can stimulate your digestion or affect the blood test results. This includes vigorous exercise, chewing gum, and smoking.  

Overall, your medical doctor should discuss the steps you need to take before your blood test. You should follow all the instructions and ensure a smooth testing process and accurate test results. If you have any more queries or want to seek quality primary care, feel free to contact Family Doctors Medical Center at 702.616.9471 or write to us

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