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Does Drinking Coffee Before Blood Test Affects The Results?

By Edited Mar 7, 2016 1 2

Patient preparation varies depending on the blood test to be done on them. Doctors instruct their patients regarding the blood test preparations to achieve accurate results. The most common preparation before blood test is fasting, which requires 6-12 hours (depending on the test) of no food and drink intake except water.  If the blood request is glucose or fasting blood sugar, the patient must be on fasting from 6-8 hours. On the other hand, cholesterol test requires 10-12 hours. However, most patients ask if drinking coffee before blood test is fine. For fasting blood requests, the answer would definitely be no. Why? Let’s discuss this further.

Coffee not only contains caffeine but also other ingredients such as sugar, milk and other artificial flavors, which can raise blood sugar and cholesterol levels if taken in by the body prior to blood extraction. Caffeine, a quick-acting drug, is easily absorbed by the body within 30 to 45 minutes. Though some people believed that black coffee, one without sugar and milk, can be drunk even in fasting state. This belief is not yet scientifically proven and experts agree that fasting still requires no food and drink intake including coffee. Nevertheless, drinking coffee for a non-fasting blood test such as electrolytes, BUN, creatinine etc., is allowed.

During fasting, no solid food and drink is allowed, even the tiniest bite from a biscuit or candy and the slightest sip from a soda could drastically increase the results. Water and regular doses of medication are usually allowed during fasting, other than medications which may affect the results of blood test. In that case, the opinion of the attending physician must be sought first to make sure that the drugs will not influence blood sugar and cholesterol levels.

Fasting provides the base line results of sugar and cholesterol levels present in the lowest amount in the body. This is done to avoid inaccurate high glucose and cholesterol results and leads to diagnosis of diabetes or hyperlipidemia, which you actually do not have in the first place. If fasting is properly done and the levels are either high and low, the diagnosis would be correct but if fasting isn’t followed, nothing is wrong with the body since glucose and cholesterol levels are naturally high when in non-fasting state. So it is important to strictly follow fasting requirements and physician’s instructions before blood test to avoid errors. Inform the physician immediately if fasting isn’t correctly done to repeat the procedure for more precise values.



Aug 8, 2011 12:39am
Interesting. I had a glass of orange juice 5 hours before a blood test and my sugar levels were high.
Sep 13, 2011 5:58pm
It's interesting to me that when a health care provider explains fasting before a blood test to mean no food or drink, some people ad lib and do as they wish. Unfortunately for them, the treatment or medication ordered because of the adversely affected blood test will be based on inaccurate information.
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