May 5, 2006
Diagnosis and Symptoms
Question from Southfield, Michigan, USA:
I am a home care nurse and my patient’s daughter/caregiver is upset with results from a fasting oral glucose tolerance test (OGTT) she had a few weeks ago. She was told that after two hours, her glucose was 290 mg/dl [16.1 mmol/L] and her insulin level was 11. She is 52 years old, thin, with no symptoms. I gave her a new glucometer and told her to check her morning blood sugars and her blood sugars two hours after every meal. I also told her to eat normally, not to avoid sugar.
After four days, her glucose has not been above 132 mg/dl [7.3 mmol/L], even after eating a meal with cake for dessert. Two hours after an ice cream, her blood sugar was 105 mg/dl [5.8 mmol/L]. I drew an A1c and it measured 5.1. One of her doctors says this is ridiculous and she has nothing to worry about. The doctor who did the test says he isn’t sure about that. He says it would be rare for both the glucose to be high in error and the insulin to be low in error. The other doctor says the glucometer testing and the A1c tell all we need to know. What do you think? Also, this girl had a terrible flu for one week about a month ago; could this have attacked her beta cells. She is also on Dilantin and thyroid medication.
Answer:
One of the causes of a false positive OGTT is the lack of adequate carbohydrate intake prior to the oral glucose load. That is why there are instructions to have the test with a three-day preparation of 100 grams of carbohydrates per day. Is it possible she did not consume an adequate amount of carbohydrates and had a false positive? Maybe. I would suggest she not just blow this off. It may be that the glucose intolerance has not occurred for a long time, which is why the A1c is not elevated. At a minimum, it should be repeated with adequate carbohydrate intake before the test.
JTL
