Taking Care: Preparing for Lab Tests

Some lab and radiological tests require adjustments to your eating or medication schedule

As a person with diabetes, you know that testing is a part of life. But some blood or radiological tests may require you to change your regular eating times or perhaps modify your medication schedule. If you have any doubts about how to prepare, check with your physician. But here are some general guidelines.

Quick tips on fasting

Your physician may order a blood or radiological test that requires you not to eat anything after midnight before the exam. That means you'll probably miss your regular breakfast. You may need to monitor your blood glucose level carefully before and after the time you normally eat breakfast to see how your body is reacting to the absence of food and any medications you normally take around the meal.

If you can, get the earliest possible appointment to shorten the time between your regular breakfast and the time of the test so you can return to your regular medication schedule as soon as possible. Waking up earlier to take a test is far less disruptive to your daily routine than having to adjust your medication.

However, if you can't avoid disrupting your meal and treatment routine, your physician may have to adjust your diabetes medication or your insulin to keep your blood glucose level stable during this period.

It's a good idea to bring your blood glucose meter and a source of sugar (glucose) to your lab or radiology appointment in case you have to wait longer than expected. If this happens and the test site is not at your doctor's office, or if the health care workers conducting the test are not part of your diabetes care team, remind them that you have diabetes. If you find yourself experiencing a hypoglycemic episode (feeling lightheaded, dizzy or sweaty), you should immediately test your glucose level, take sugar or glucose if necessary, and notify the nurse or lab technician.

What to do about injected contrast substances

Some diagnostic X-ray tests require intravenous (IV) injection of an iodine-containing a substance (sometimes erroneously called "dye") that creates contrast on the X-ray image to help determine if there's anything wrong with a certain organ or system. Many people will be able to continue their medications as usual for this procedure.

However, if you are taking metformin and need an IV contrast substance, notify your physician and radiologist before the test. Certain combinations of IV contrast substances and metformin can cause kidney problems. In addition, you may not be permitted to take your metformin for several days after receiving such an IV contrast substance. Talk to your doctor about this. You may need a different diabetes medication or insulin to keep your blood sugar under control during this period.

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