Drinking coffee in the morning is a common routine for many of us, and many people enjoy coffee throughout their day.
If your doctor has ordered a blood test for you, you might be wondering if you can still drink your usual cup of coffee.
In this article, we’ll talk about which blood tests you should skip your coffee for and which ones won’t be impacted by drinking coffee.
Can you drink coffee before a blood test?
If any of the blood tests you’re having done requires fasting, then you shouldn’t drink coffee beforehand. Fasting blood tests recommend 8-12 hours of fasting before the test, which means only drinking water.
If your blood test doesn’t require fasting, then it’s generally considered fine to drink coffee before it, whether it’s several hours before the test or immediately before.
How can coffee affect your blood test results?
Drinking coffee can impact your blood test results because it contains compounds that your body metabolizes. Even black coffee contains oils and very low amounts of carbohydrates and protein.
Coffee typically contains caffeine, which impacts blood tests in several ways. According to a study, caffeine ingestion negatively impacted the results of glucose and insulin tests.
Researchers note that caffeine appears to negatively impact insulin sensitivity among participants who are lean, obese, and those who have type 2 diabetes.
If you drink coffee with sugar, milk, or cream, it’s even more likely to affect your blood test results. Tests that measure the fat in your blood (such as cholesterol and triglycerides) and tests regarding glucose tolerance likely won’t be as accurate if you consume fat, carbohydrates (from milk), and/or sugar in your coffee.
Why might you need to fast before a blood test?
Your healthcare provider or laboratory technician can tell you if you’ll need to fast before your blood test.
You might need to fast before tests that measure baseline levels of things like cholesterol and blood sugar, which are impacted by your diet.
Some blood tests that aren’t impacted by your diet don’t require fasting, such as the hemoglobin A1c test, blood count tests, renal function panel, pregnancy tests, and many others.
Blood tests can provide useful information to diagnose potential health problems. It’s important to follow your provider’s instructions to ensure your blood tests are as accurate as possible.
What kind of blood tests require fasting?
Fasting blood glucose
A fasting blood glucose test measures your blood sugar level when you haven’t had anything to eat or drink (besides water) for at least eight hours.
A fasting blood glucose test is used to determine if you have altered glucose metabolism, which is used to diagnose prediabetes and both type 1 and type 2 diabetes.
If your fasting blood glucose level is above 100 mg/dL, it’s considered abnormal. If you drink coffee before this test, it might be falsely higher. So you might not have blood sugar problems, but the reading signifies that you do.
RELATED: Newly Diagnosed Diabetes: What To Know.
Lipid panel
A lipid panel includes tests like total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides.
Your healthcare provider might recommend that you have a lipid panel done if you have a history of high cholesterol, to screen for high cholesterol, if you have heart disease or diabetes, or to re-check your lipids if you’re taking cholesterol medications.
Drinking coffee might elevate your lipid levels, especially if you have fat or sugar in your coffee. Some healthcare providers might not require you to fast for a lipid panel, especially if you don’t have a history of high cholesterol or triglycerides.
However, some practitioners suggest that the burden of fasting on patients (e.g., you might need to return to the clinic for blood work vs. being able to do it when you’re already in the office) might be too great to recommend fasting for lipid testing, considering the little difference that can result between non-fasting and fasting testing.
When in doubt, ask your healthcare provider if they recommend that you fast for your lipid and cholesterol tests.
Basic metabolic panel
A basic metabolic panel measures several things, including your glucose (blood sugar), electrolyte levels, and some markers of your kidney function. It’s typically recommended to fast before a basic metabolic panel.
Oral fat tolerance test
An oral fat tolerance test measures your body’s response to eating a large amount of fat, usually around 75 grams.
Similar to a glucose tolerance test, an oral fat tolerance test measures the rise in things like triglyceride levels in response to eating. Altered fat metabolism is thought to occur more in people with metabolic syndrome and might help diagnose the condition.
Glucose tolerance test
A glucose tolerance test is most often used during pregnancy to diagnose gestational diabetes, which is diabetes that occurs when you’re pregnant. Glucose tolerance tests can also diagnose blood sugar problems in people without diabetes.
During a glucose tolerance test, you’ll be asked to come fasting. Your blood sugar will be measured while fasting, and then you’ll drink a sugary solution containing 50-100 grams of sugar.
Your blood sugar levels will be measured one hour after drinking the sugary drink for a one-hour glucose test and again at two and three hours for the 3-hour glucose tolerance test.
If your blood sugar levels are elevated at 1, 2, or 3 hours after drinking the sugary drink, you might be diagnosed with gestational diabetes.
Fasting insulin test
Insulin is a hormone that helps lower your blood glucose levels. With conditions like prediabetes and type 2 diabetes, insulin resistance is often present. Insulin resistance means your body doesn’t effectively use insulin, which can cause elevated insulin levels.
You’ll need to fast before a fasting insulin test so your levels aren’t falsely high, since your body releases insulin in response to eating.
Liver function test
Liver function tests can be impacted by eating and taking certain medications. Your healthcare provider might advise you to stop taking any over-the-counter or prescription medications in addition to fasting to measure your liver function.
Conclusion
Drinking coffee, whether black or with additions like milk, cream, or sugar, can impact the results of certain blood tests.
You should avoid drinking any coffee for blood tests requiring fasting (no eating or drinking anything besides water for 8-12 hours).
Many blood tests that aren’t impacted by your diet don’t require fasting, so drinking coffee wouldn’t impact their results.
When in doubt, ask your healthcare provider or lab technician if you need to be fasting for your blood tests.
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