# B12 blood test - to fast or not to fast?



## nitty

Does anyone know whether fasting is essential before having a blood test for vitamin B12 levels?

I had it checked last week for the first time, and it was just added onto my other routine bloods (I'm on azathioprine) and so I didn't do anything differently.  
It was only when I was looking up the normal values online that I got the impression that I should have fasted for about 8 hours beforehand.  However, I can't find many websites that specify this, and nobody mentioned it to me when I booked the test or had it done.  Even worse, I had taken my multivitamins that morning, too!

My IBD nurse has suggested I retake the test, especially because of the multivitamins.  I am booked to have it done tomorrow (although it's at lunchtime, so I'll be starving by then!).

I just wondered if anyone else who has had their B12 tested was told to fast beforehand?

Nitty


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## CrohnsChicago

Sometimes you can call the lab beforehand and they can tell you but usually it depends on what your doctor tells you. Be sure to get clear instructions from your doctor if the lab cannot provide you with any info

CORRECTION:

I found the following article that indicates you should fast: http://health.nytimes.com/health/guides/test/vitamin-b12-level/

Fasting is commonly used for the following tests:

http://www.ehow.com/about_5244459_blood-tests-need-fasting-preparation_.html

I personally wound up fasting for my B12 blood test because I did that test the same time I did the ones mentioned in that link provided.


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## If*

I never fasted for it?


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## nogutsnoglory

I have only fasted for cholesterol blood tests.


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## Lustforlife

I did not need to fast for vitamin tests (b12, d, iron) but did need to fast for tests of blood sugar /glucose levels, or anything that measures digestive enzymes (like cholesterol)

When I walked into my appt where I was having the vitamins tested the nurse asked how I was doing and I said ok just really hungry! She gave me a strange look and said ...why, did you skip breakfast? You didn't need to.


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## HalfHeartedHeroine

Lustforlife said:


> I did not need to fast for vitamin tests (b12, d, iron) but did need to fast for tests of blood sugar /glucose levels, or anything that measures digestive enzymes (like cholesterol)
> 
> When I walked into my appt where I was having the vitamins tested the nurse asked how I was doing and I said ok just really hungry! She gave me a strange look and said ...why, did you skip breakfast? You didn't need to.


That was the exact response I got at my last blood draw! lol It's not like I can un-eat breakfast, so better safe than sorry!


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## nitty

Thanks everyone.

I'm staying off the food anyway just to make sure.  It will be interesting to see whether there is much difference in the results.

Nitty


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## DustyKat

You do not need to fast for B12 and fasting will not affect the result.


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## Paranda

Does taking vitamins containing B12 interfere with the test results ?
Should you stop taking them a few days before just in case. 
Talking about just a regular B complex or multivitamin tablet taken once a day. 
Thanks.


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## nitty

The main reason for re-testing me is that I'd taken a supplement with lots of B vitamins (similar to Berroca) about 3 hours before the test.  I'm fasting anyway just in case, as it's the laboratory websites that recommend it for a more accurate result.

I'll let you know if there's any significant difference in the results.


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