By Michael P. Kosty, MD

Question: “I am a diabetic and I am a breast cancer survivor. While I was undergoing my chemo treatments some of the drugs they gave me really affected my blood sugar. It would really stress me out. My doctor said to just ‘ride it out.’ Also when I had a CT scan and they injected me with the dye, I had to quit taking the Glucophage for a few days, which caused my blood sugar to rise. Have there been any studies done on this issue?”
— Mary Nachreiner
Anaheim, California

Answer: Elevated blood sugar and difficult-to-control diabetes are frequent but temporary side effects associated with chemotherapy. The most common cause is the use of Decadron^® (dexamethasone), a steroid, as premedication for chemotherapy. Decadron is a required premedication for patients receiving Taxol® (paclitaxel) or Taxotere^® (docetaxel). It is also commonly given intravenously as part of the antinausea therapy.

Steroids raise blood sugar in everyone, but in someone who is diabetic, blood sugar can become very elevated, as it did in your case. If you are a diabetic patient receiving chemotherapy, it is vital that your diabetes doctor coordinate with your oncologist regarding management of your diabetes. While uncommon, it is possible that blood sugars that are excessively elevated can make chemotherapy side effects worse. At a minimum, high blood sugar will diminish your energy. It could result in you becoming dehydrated and developing kidney damage.

During CT scans, a dye (contrast material) that contains iodine is often administered intravenously. The dye makes blood vessels and certain structures or organs inside the body more visible on the CT scan pictures. The dye may be used to evaluate blood flow, detect some types of tumors and locate areas of inflammation. The contrast material used during CT scanning can on rare occasions cause water loss or damage to the kidneys that may lead to kidney failure. This is a concern if you have poor kidney function, dehydration or diabetes, especially if you take Glucophage^® (metformin) to control your diabetes.

To minimize this risk, most patients are instructed to temporarily stop their Glucophage, which can lead to an elevation of your blood sugar. Increasing your fluid intake will minimize any kidney damage. Again it is important that your diabetes doctor be aware of any change, however temporary, in your diabetes medicines.

As a sidenote, if you have a history of kidney problems, blood tests (creatinine, blood urea nitrogen) may be done before the CT scan to check that your kidneys are functioning properly.

--Michael P. Kosty, MD, CURE editorial board member, is a medical oncologist at Ida M. and Cecil H. Green Cancer at Scripps Clinic in La Jolla, California.