Can I Drink Coffee Before a Blood Test?

Yesterday, you went for a blood test and discovered you were low on iron. Your doctor told you to drink less coffee to help your body absorb the iron better. Can you drink coffee before a blood test? The short answer is no. The long answer, though, is a little more complicated.

However, you might want to read this article if you are an avid coffee drinker and you simply have to get your coffee fix in the morning before a blood test.

Here’s what you need to know about coffee and blood tests.

Is it OK to have coffee before blood work?

The short answer…

Yes, in most situations, before a “fasting” blood test, you may drink black coffee. some doctors say yes to black coffee, even before a cholesterol test as long as you don’t add cream or sugar.

In general, these drinks do not affect the results of typical tests in the fasting laboratory, such as cholesterol (lipid panel), metabolic panel, or blood glucose. We’ll get to which blood tests might need total fasting.

However, coffee influences digestion and can influence the outcome of a blood test as well. As such, prior to a fasting blood test, people do not drink coffee.

The definition of fasting should be clarified by your doctor!

How does coffee affect blood test?

Coffee will interfere with blood test results even though you drink it black. This is because it contains caffeine and soluble plant matter, which could distort the results of your examination. Coffee is also a diuretic, which means it helps you pee more often.


Coffee is also a diuretic, which means it’s going to improve how much you pee. This may have a dehydrating effect. The less hydrated you are, the harder it will be for a nurse or other medical professional to test your blood for a vein. This can make the blood test more complicated or more painful for you.

The difference between fasting and non-fasting blood panels

Blood tests differ depending on what the doctor checks and what the criteria are for each blood test. Blood tests are basically broken down into two distinct groups. Non-fasting or fasting. Depending on the test you have carried out, the answer to whether or not you can drink coffee could be in one of these two categories.

Fasting Blood Panels:

How long should you fast before a blood test? These blood panels look at certain levels, and these tests usually require the patient to refrain from eating or drinking any kind of food 8 to 12 hours prior to testing. The explanation for this is that, depending on the examination, coffee will change the numbers in particular and decrease the blood panel’s accuracy.

For fasting, the blood panels are:

  • Basic Metabolic Panel (BMP): This focuses on diabetes and kidney function. Most of the time, you’re going to fast for this test.
  • Comprehensive Metabolic Panel (CMP): This is a more detailed blood panel that looks at different things in your blood, such as electrolytes, blood proteins, blood sugar, kidneys, and liver, to see where your body works. You’re definitely going to be fast for this panel.
  • Glucose: This is a test to see where your blood sugar level is. It is recommended that you fast 12 hours before this test. Caffeine should be avoided in particular because caffeine may affect blood sugar levels and may increase blood sugar levels.
  • Lipid profiles: This is your overall test of cholesterol. This one needed fasting because the lipid is fat in the blood. When cholesterol screening is done, anything you eat or drink, including coffee, can affect your triglycerides and lipid numbers. Doctors really want you to drink water only if you have to take this test. This is one of the tests that I personally did.
  • Gamma-glutamyl transferase (GGT) test: This test tests the amount of GGT enzyme in your blood that may suggest liver disease. It is typically important to avoid alcohol for up to 24 hours beforehand; in addition, you may or may not be expected to avoid food for up to 8 hours before the test.
  • Other nutritional tests: Blood tests that quantify vitamins and minerals (such as iron) also require early fasting. Depending on the form of nutritional testing, you might be asked to fast for 6-12 hours before the test.

Other fasting panel blood test that requires fasting:

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

Non-Fasting Panels:

Non-fast blood panels are panels where it doesn’t matter what you eat or drink before you do it. Nothing you’re taking is going to affect your numbers coming back. You can drink as much coffee as you want. Your blood test will not hurt.

Non-fast blood tests are as follows:

  • Amylase: It’s looking for pancreatic diseases. For this one, there’s no fasting. You can eat or drink whatever you like.
  • Antinuclear Antibody (ANA): This is a blood test for Lupus and other autoimmune diseases. If the sample is used only for an ANA test, you can eat and drink normally before the test. If your blood sample is used for additional testing, you can need to take a short time before the examination. Your doctor will give you instructions
  • Activated Partial Thromboplastin Time (APTT): This is a blood test that tests your risk of excessive bleeding or lack of a clotting factor right before you start surgery of some kind. Usually this test is run days before surgery, so you can have a cup of coffee. But be advised whenever you have any kind of surgery, the doctors will advise you to fast and not eat or drink anything after midnight before the surgery. The reason for this the anesthesia. It can make people sick when they get out of it if you eat or drink anything.
  • A1C: This is another test for diabetes or prediabetes. Strangely enough, fasting is not needed for A1C since the test tests the average blood glucose levels over the last three months.
  • Electrolyte panel: This is looking at the balance of your electrolytes and electrolytes. Food and drink, coffee in particular, there is no evidence of a fluid-electrolyte imbalance
  • HIV Antibody: This is the HIV or AIDS panel. There’s no need for fasting, since it’s only detecting the actual virus. Although studies have shown that higher caffeine intake was associated with higher CD4 cell counts and lower HIV viral loads, suggesting beneficial effects on the development of HIV disease. Food for thought, nothing more.
  • Lyme Disease: This is searching for susceptibility to Lyme Disease or Lyme Disease. You don’t need to fast..
  • Mono: The mononucleosis test is used to help decide whether a person with symptoms has infectious mononucleosis (mono). The test is used to detect proteins in the blood called heterophilie antibodies that are formed by the immune system in response to Epstein-Barr virus (EBV) infection, the most common cause of mono-infection.

What if i accidentally eat or drink before my blood test?

If you have been told to fast before the blood test and you mistakenly eat or drink something during the fasting window, it is necessary to tell your health care provider or the person taking your blood. If you don’t, the findings may be wrongly interpreted.

It could be possible for your healthcare professional to interpret the non-fast test results. Most likely, you will be told to reschedule the blood test for a time when you will be able to complete the test quickly.

Your doctor will let you know what steps you need to take before you take a blood test, including whether or not fasting is needed and for how long. By following all test directions and best practices (including how to fast), you will ensure that the test process is smooth and that the results are as reliable as possible.


Coffee can relax your nerves before a blood test, particularly if you have fear for needles. But drinking coffee when required to fast can really screw up your performance. That means another ride to get more blood drawn if you don’t listen to your doctor’s instructions.

Make it easy on your own. Do your study and see which blood tests are being carried out, as you might need to do other tests. If you need fasting, please make it easy on yourself and quick. After the exam, you can still go for the rewarding cup of coffee. If you don’t have to fast, drink as much coffee as you want!


Self-proclaimed coffee drinker. I would, on a typical day, start my day by grinding my coffee with a manual grinder and use a French Press as a starter (2 cups), then a pour-over in the afternoon (4 cups). I had my fair share as a barista but I prefer to drink it, not serve it.