Analyzing a simple blood sample can provide such a deep insight into your health.

It’s a quick procedure, efficient, affordable, and helps you prevent more dangerous diseases. Best of all, you can order blood tests from reputable sources online. You are mailed a form which allows you to draw blood at a nearby clinic or lab. Your blood is analyzed, and the results are sent to you in a few business days.

There is also a plethora of useful blood tests you can try to gauge your health. For example, you can find out if you have a high sugar level in the blood, how are your thyroid hormones doing or how much protein you have in your bloodstream. Many of these tests also require fasting, and this is something you need to know before doing the test.

Why Should I Fast Before Doing a Blood Test?

People should fast before doing a blood test because certain foods and drinks can influence the hormonal levels in the bloodstream. As a result, the fasting blood tests results will not be accurate, and the doctor might set an incorrect diagnosis.

For example, if you eat something, anything, and then do a blood glucose test, the chances are that the levels of sugar in your bloodstream might be very high. According to your blood test results, the doctor might declare you as a person with diabetes.

That’s because the body has processed the food and transformed it into glucose. This glucose should be absorbed by cells and to do that, the pancreas secretes insulin. In a couple of hours, the insulin has allowed the cells to absorb the sugar in the blood. Your glucose levels will come back to normal.

Now you probably understand why it’s mandatory to fast before specific blood tests. It will help the doctor establish the typical hormonal values in your blood. If these values, found during a fasting state, are not within normal ranges, then you might get treatment depending on your ailment.

What Are the Most Popular Fasting Labs?

At this moment, you’re probably wondering “what blood tests require fasting.” Well, not all blood tests, but some of them certainly do. Here are a few blood tests which require fasting.

Not all blood tests will require you to fast beforehand. Blood tests that you will likely need to fast for include:


  • blood glucose test
  • liver function test
  • cholesterol test
  • triglyceride level test
  • high-density lipoprotein (HDL) level test
  • low-density lipoprotein (LDL) level test
  • basic metabolic panel
  • renal function panel
  • lipoprotein panel

1. Blood Glucose Test

This is one of the most popular tests, and it works as described above. It helps the doctor determine the actual sugar level in the body. Patients are required to avoid eating or drinking anything than water for at least 9-10 hours before doing the test.

2. Cholesterol Test

Measuring the cholesterol levels in the body is paramount to determine different types of diseases, particularly cardiovascular ones.

The cholesterol is a waxy substance lining the interior of blood vessels. It's required to keep the blood vessels flexible. However, too much cholesterol can cause blockages in veins and arteries. A surefire sign of high cholesterol levels is high blood pressure.

Cholesterol breaks down into two essential categories - LDL and HDL. LDL cholesterol is commonly known as the “bad” one, meaning that having high levels of LDL cholesterol is unhealthy.

HDL cholesterol is considered to be the “good” one. Having high levels of this type of cholesterol is a good thing. A standard blood test can measure both HDL and LDL cholesterol levels. Based on this data, the doctor can make recommendations, usually related to your diet and exercise regimen.

3. Triglyceride Test

The triglycerides are a type of fat cells found in any human body. They are similar to cholesterol but have a different function. For example, the cholesterol is used to build cells and it plays a vital role in the production of hormones. The triglycerides are used to produce energy when necessary.

Each person burns down calories during the day. Any calories from foods or drinks which haven't burned are transformed into triglycerides and stored in the fat cells. When the body requires more energy, it breaks down fat cells and converts the triglycerides stored there.

However, having too many triglycerides in the body can be a bad thing. That’s because they are responsible for thickening the arterial walls, causing high blood pressure and heart disease. In the long run, very high triglyceride levels can lead to heart attacks and other cardiovascular problems.

4. Liver Test

Your liver is responsible for approximately 500 bodily functions, according to some recent studies. Its main job is to detoxify your blood and help with metabolic and digestive processes.

Fasting is required before doing a liver blood test to prevent dietary substances to interfere with blood hormones. A liver test can show if a patient has liver damage if the liver produces the right hormones and in the correct quantities, the number of B vitamins stored in the liver, whether the patient has some form of hepatitis, etc.

5. Metabolic Panel Test

A metabolic test implies testing different types of enzymes, electrolytes, and hormones in the body. Some of the substances tested include sodium, potassium, albumin (a protein), bilirubin, calcium, carbon dioxide, alanine transaminase, and more.

Keeping some of these substances balanced is very important. For example, having too much sodium in your body can make your blood acidic, a condition which can lead to various diseases. Similarly, having a calcium deficiency can lead to bone density loss and a predisposition for fractures and osteoporosis.

You need to fast before doing a metabolic blood test because some foods contain the substances you’re going to be tested for. Eating or drinking anything else than water before a metabolic test panel can drastically influence the results in a wrong way, leading to an incorrect diagnosis.

6. Kidneys Test

The kidneys are other essential organs in the human body. Just like the liver, they are responsible for filtering out toxins and eliminating them from the body. The kidneys also perform a wide variety of functions, and they are capable of doing the work of other organs if these are injured.

A kidney blood test measures various important substances and hormones in the kidneys. For example, the glomerular filtration rate determines how good your kidneys are at filtrating toxins, and this is one of the things measured by the test. You’re not allowed to eat or drink anything except water before the test to avoid overloading the kidneys.

7. Iron Blood Test

All humans require small amounts of iron in the bloodstream to remain healthy and have energy throughout the day. An iron blood test measures the amount of iron stored in the body. If you’re deficient in this mineral, you might develop anemia, which is a condition characterized by excessive fatigue.

Iron is usually found in a plethora of foods. Eating some of these foods before a test can temporarily raise your iron levels and lead to a false diagnosis. That’s why you’re required to fast for at least 8-10 hours before doing an iron blood test.

At the same time, keep in mind that some of the supplements you take, such as multivitamin can contain iron in various quantities. You should discontinue supplementation with these vitamins and minerals for at least 1-2 days before doing the test.

8. Vitamin B12 Test

The vitamin B12 is also known as cobalamin, and it’s involved in the metabolism of almost all cells in the human body. It is present in many foods and beverages, so it’s easy to get a high amount of vitamin B12 in a single meal, especially if you eat a lot of vegetables and legumes.

This vitamin is also crucial for the nervous system. People deficient in vitamin B12 and the other vitamins in the B complex usually develop diseases related to the activity of the nervous system. Patients are required not to eat foods or drink beverages for at least 6-8 hours before doing a vitamin B12 blood test.

9. Heavy Metals Panel

You can also perform a test to detect the number of heavy metals you have stored in your body. There are several important metals which can seriously affect your health if they are in elevated quantities. For example, arsenic, mercury, cadmium, and lead are popular heavy metals found in the human body.

Some of these metals circulate in the bloodstream while others attach to bones and organs. In large quantities, these metals can lead to poisoning and even death, in extreme circumstances. By doing a blood test, you can discover how serious your heavy metal problem is and see if you need treatment or detoxifying.

You are not allowed to eat or drink because some foods contain heavy metals. For example, sardines contain a lot of arsenic, regardless of their origin. Other seafood and fish also contain high amounts of mercury. Patients should fast for at least 8-10 hours before doing the heavy metal blood test.

10. Hormone Tests

Food can increase insulin blood levels that can decrease hormones like testosterone, IGF-1, thyroid, and others. 

Fasting Q&A - Answering Some of Your Questions

Now you know what blood tests require fasting and have a broader understanding when it comes to lab tests. There are a lot of questions related to fasting in general, and it’s essential to address them in this article, so you have a better understanding of this subject. For example:

1. Can I Drink Coffee, Alcohol, or Smoke During My Fast?

No, you are not allowed to drink coffee, not even a black one without sugar. That's because coffee contains enzymes which stimulate your liver and can influence your hormonal balance. You should refrain from drinking your morning coffee before doing a blood test.

When it comes to smoking, that isn’t allowed either because it can mess up with your glucose levels and increase the amounts of heavy metals in the body. Best of all, quit smoking altogether, and you’ll be much healthier.

Regarding alcohol, you should also refrain from drinking any alcoholic beverages. That’s because alcohol can increase your glucose levels and cause inflammation in your body. Patients shouldn’t drink alcohol for at least 1-2 days before doing a blood test as it takes a while for the body to eliminate this substance.

2. Can I Chew Gum or Brush My Teeth Before the Test?

Chewing gum is not allowed because it determines your body to produce digestive fluids. At the same time, the sweetness of the gum can interfere with the blood sugar level. Don’t chew gum, but you can brush your teeth, as long as you don’t swallow anything. Swallowing toothpaste can start the production of hormones and enzymes in your body, so be mindful of that.

3. Can I Exercise While I’m Fasting?

Ideally, no, unless you’re doing very light exercises without using weights.

That’s because exercising usually increases the inflammation level in your body. For example, heavy exercises such as lifting weights or sprinting can elevate the levels of C-reactive protein in the body. This is a marker of inflammation, and if you’re doing an inflammation panel, the results will be inaccurate.

At the same time, vigorous exercise can also increase your testosterone levels for a while as well as your levels of human growth hormone. If you test for these hormones, your results will be incorrect, and the doctor's diagnosis will also be wrong. On top of that, exercising makes you hungry, and since you're fasting, you're not allowed to eat anything. Not eating after a workout session can cause dizziness and other problems, so it's merely better to skip the gym in the day before doing a blood test.

4. For How Long Should I Fast?

As a general rule of thumb, you should fast for at least 8 hours before doing a blood test. Most doctors schedule these tests early in the morning so that you will be asleep most of this time. In some cases, you might need to fast for 10 or even 12 hours, but this will be communicated by your doctor. You might also need to discontinue supplementation with biotin for 72 hours before doing a blood test.

5. What If I Ate Something During My Fast?

It happens for patients to forget that they are fasting and accidentally eat something or drink milk, coffee, or other beverages. This is not a significant problem, but it’s imperative that you notify the healthcare provider before doing the test. He or she will take this into account when interpreting the blood test results. In some rare cases, it might be possible to reschedule the blood test.

6. Should I Take My Meds/Vitamins During My Fast?

As a general rule of thumb, the answer is no. That’s because your meds and supplements might contain substances which interfere with the hormones in your body. Therefore, the test results will be affected, and the diagnosis will be inaccurate.

Speak with your physician and let him know exactly what meds and vitamins you take. Ask if you need to discontinue supplementation with these drugs during your fast, and you’ll know exactly what to do.

Get Your First Blood Test Today!

Did you know that you can get fasting blood tests directly from the internet these days? These tests are called direct-to-consumer labs and can be bought at affordable prices. You don’t need a doctor’s appointment or prescription and you get your results back within a few business days.

Visit and check out the popular blood tests listed there. Some of these blood tests might require fasting, and all of them will help you gauge the state of your health.