Doc: Doctor must do pre-PET insulin pump instruction

Keith Roach
To Your Health

Dear Dr. Roach: My wife is a Type 1 diabetic. She uses an insulin pump to control her sugar. She needs to have a PET scan. The prep for this test is fasting for six hours prior, along with no insulin for six hours. She was told to turn off her pump. Her blood glucose must be 150 or lower for the test. Even when she has fasted for 12 hours and her blood glucose is at 116, with her pump off, two hours later her BG is over 200. How do we get this test done?


Dear S.L.H.: An insulin pump is a programmable device that continuously injects a variable amount of insulin just below the skin, where it quickly enters the bloodstream. It most often is used by Type 1 diabetics, where it is often the most effective way of managing blood sugars, especially in people who have had trouble controlling their sugars with other means.

The insulin used in an insulin pump normally is very short-acting, so a few minutes after the pump is shut off, the blood sugar will start to rise. Since that is extremely dangerous in people with Type 1 diabetes, I would suggest a dose of longer-acting subcutaneous insulin before the pump is turned off.

I must emphasize that insulin pumps are prescribed and administered only by experts, and that almost always means endocrinologists, who specialize in diabetes. Thus, only her endocrinologist should be the one giving orders on the insulin pump and on subcutaneous injections (if her diabetologist agrees with me).

A PET (positron emission tomography) scan is used to find areas of high metabolic activity, usually in people with suspected cancer. A radioactive analogue of sugar, usually fluorodeoxyglucose, is injected and will be taken up by cells that use a lot of sugar, which includes most cancer cells. A person needs to be very still after the injection, or the muscles will take up the FDG, which may confuse the results.

However, the cells are less likely to take up FDG in people with high blood sugar, which is why the blood sugar needs to be well-controlled (usually below 150, as you were told).

I hope the results for your wife are favorable.

Dear Dr. Roach: I found your response to the male with shingles after he received the vaccine disturbing. I received a shingles vaccine quite a number of years ago, and am fearful of getting shingles. Do you recommend getting another shot?


Dear F.C.P.: Some individual doctors getting a booster shot for shingles, since a recent study shows its effectiveness does seem to wear off after eight years or so, but that is not yet a general recommendation. The guideline writers are awaiting results of ongoing studies. A newer type of vaccine is in development.

The current vaccine is not indicated as a booster, but for people who are very worried about shingles, it wouldn’t be unreasonable to repeat the vaccine at age 70, for example, if you were vaccinated at 60.

The major downside is the expense, since it is costly and would likely not be covered by insurance. Still, I don’t recommend a booster shot in general. until we have more information.

Email questions to