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February 1, 2006

Diagnosis and Symptoms

Question from Glasgow, United Kingdom:

I would be extremely grateful if you could offer your opinions on the following and whether you think that I should go back to my doctor. At 5 feet, 5 inches tall, I weigh approximately 8 stones (112 pounds). I am 33 years old and recently went to the doctor because of irregular skin pigmentation on my face. The doctor diagnosed it as vitiligo and said he wanted to run some blood tests for autoimmune diseases as these could be linked to it. I had a fasting blood test which showed that I had a blood sugar level of 7.5 mmol/L [135 mg/dl]. My doctor called me back in order to have another fasting blood sugar test as it was so high, and also an A1c test. The results of the second test was 5.5, but I don't know if this was my blood sugar or my A1c as I did not speak to the doctor himself. Anyway, I was told that no further action need be taken as this fell within "normal levels" and that I did not have diabetes. I am, however, a bit confused as looking through some web sites on the Internet, they seem to say that a fasting blood sugar level of 7.5 mmol/L [135 mg/dl] is, in itself, a sufficient basis for a diagnosis of diabetes/pre-diabetes, or, at least, for preventative dietary precautions and/or further investigations to be taken. So, I do not understand why I have now been told it is okay. If it were 7.5 mmol/L [135 mg/dl] fasting, then surely this is an issue? I am obviously concerned about such a high level. On the day prior to the first test, I had not felt very well and had barely eaten or drank anything all day, until around 8.45 p.m. when I drank around 1 litre of pure orange juice shortly before going to bed. I then fasted overnight until 9.30 a.m. the next morning, which is the required 12 hours for the fasting test. Could the orange juice at this time of night (combined with little food during the day) have skewed the first test result to an unnatural high? I usually drink about 1 litre of orange juice daily, but rarely all at once. Before I had the next test done, someone told me that citrus fruits and other vitamin c containing preparations can actually skew a blood glucose test and should be avoided for 36 hours before the test. So, for this length of time, I avoided all fruit juice, fruit, etc, drinking only water alongside my usual meals and the second test showed normal levels. However, please note that when I cut out all fruit juices for the second test, I felt that my blood sugar levels were going quite low as I started to feel shaky (which has happened to me many times in the past) and I had to correct this with a biscuit and some carbohydrates which seemed to regulate it. My point here is that I did feel that my blood sugar levels were abnormally low due to cutting out the juice. Could I also, therefore, have inadvertently "skewed" the second test result to an unnatural low by cutting out all fruit juices (which is not normal for my diet) and thus the doctor's decision not to proceed any further? I understand that an A1c test measures glucose levels over a period of time, so, could the temporary blip of 7.5 mmol/L [135 mg/dl] on this occasion be overlooked? I would be very grateful for a reply as this is causing me considerable concern.


The diagnosis of diabetes is not dependant on the hemoglobin A1c. Although your value is normal at 5.5%, you have one value you cannot wish away. The second value was more in line with your A1c. What to do now? First, I would consider having another fasting glucose or even an oral glucose tolerance test. The oral glucose tolerance test can settle the score in one day, whereas the diagnosis of diabetes with fasting glucose levels requires elevated glucose levels on more than one day. If you do opt for the oral glucose tolerance test, it is very important that eat 100 grams of carbohydrate for several days prior to the test to avoid a false-postive test. I hope your tests will demonstrate you do not have diabetes and that the one value was an artifact. However, care should be taken to make sure that is the case.