Does drinking black coffee prior to a wide spectrum blood test change the outcome?

Does drinking black coffee prior to a wide spectrum blood test change the outcome?

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  1. It really depends on how much you drink and which specific tests they will be running. Drinking a cup of coffee an hour before blood draw will do nothing to cell counts, hemoglobin, and related things. It will not make any substantial changes to albumen or other proteins. It will not impact blood gases(if they are actually testing for that—it’s pretty rare they do).
    If a full lipid panel is being run, a big enough dose of coffee can alter triglycerides a bit, because coffee helps to release them into the bloodstream (it’s one of the reasons some long-distance athletes drink coffee just before an event). Anything using triglycerides for computing lipid ratios will be thrown off.
    Blood sugar analysis (glucose concentrations and A1C) can be diddled with a bit by a large dose of Coffee close to the time of blood draw, but a single, small cup hardly changes any sugar results—unless you doctored the coffee with sugar. If you did, you will skew some of the possible sugar tests, although A1C will not be dramatically affected, since it is a measure of medium to long-term sugar (glucose) levels.
    In general, it is simply best to not take in anything but water just before a blood draw. If you made an error and had a small cup of Joe just before the draw, tell them and they will know whether or not it will make any difference for the tests you have slotted for your blood.

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  2. Caffeine in general can give you falsely high fasting blood sugars. My diabetic brother told me this; after that, I held off any coffee until after my blood test, and my fasting blood sugars were INDEED down in the normal range after I did that.

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  3. In most blood tests, you are specifically told NOT to drink anything except water. Unless that was NOT a specific instruction, caffeine is generally not a good idea.

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