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PET Scan

lisabnc's picture
Posts: 1
Joined: Nov 2007

Does anyone know why you have to follow a low carb diet on the day before your PET scan? I have one tomorrow and they said low carb, no gum, no hard candy, no excercise of any kind the day before on my paper...just curious.. Thanks in advance!

vinny3's picture
Posts: 933
Joined: Jun 2006

For the PET scan they feed you some radioactive-tagged sugar. The idea is that cells that metabolize at a faster rate (such as cancer cells but also recent healing surgery sites) will take more in and thus "light up". If you load up those cells ahead of time they may not take as much and would not light up. Prohibiting the exercise may be so that you don't injure a muscle or area of the body as that could make that area light up as well.


KathiM's picture
Posts: 8077
Joined: Aug 2005

I LOVE our 'resident doctor'!!!! You explain things so well, Dick....thank you!

Hugs, kathi

Betsydoglover's picture
Posts: 1256
Joined: Jul 2005

Hi -
I also read / was told that any muscle activity, even without injury can show up on PET. In particular, heavy exercise can result in increased uptake in the heart, making it difficult to detect any lesions that may exist near the heart. Apparently, caffeine can also cause this effect because it increases heart rate. I always have my PET's in the mid morning and refrain from any food after about 7PM the previous evening, while eating "moderately" the previous day - good mix of carbs/protein - relatively low glycemic load eating. The idea is to make sure your blood glucose levels are not high, so that any cancer cells uptake the radioactive glucose and not the excess you just consumed yesterday.

False positives with PETs may be disturbing, but false negatives are way worse - so the low activity, low carb day before the scan helps to ensure more reliable results.

Take care,

Posts: 1048
Joined: Jan 2007

This is why I am so grateful for this site. Someone always has information to share. I wasn't aware of this and I don't believe my hubby did any "fasting" before his PET when we first started this battle. I'm sure he will be having a PET again in the future, so thanks for asking the question and thanks to those knowledgeable folks out there for the answer! God Bless and I wish you an all clear on the scan. Keep us posted.

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