From the U.S. Navy:
My daughter is 6 years old and has diabetes for the last two years. She recently switched to a new endocrinologist. The new doctor did an A1C test at his lab. She was 9.8 on scale of 5 to 9. Only 15 days before that, she had an A1C test done at another lab. She was 8.4 on a scale of 4 to 5.8. The doctor converted this result to the other lab's scale and said that it is 13.0 on their scale. (I think he did the following calculation 8.4/5.8 * 9 = 13.0.) So on the same converted scale of the first lab she was 13.0 and after 15 days she was 9.8. The doctor said that he can not explain why the results are so different and that he trusts his lab's results and will go with that.
Her daily blood reading during three or four months before taking the test were very consistent and she never got sick during that time. I cannot think of any thing that her result should be so different. I'd like to know that how reliable these A1C results are, and if I should insist the doctor or the labs investigate this further.
This question was referred to all our endocrinologists, who have each given an answer:
Answer from Dr. Lebinger:It is very difficult to compare results of Hemoglobin A1C's from different laboratories. Not only can their "normal" or non-diabetic ranges differ, but how rapidly the result rises above the normal range can vary from one lab to another. For instance 1 point above the non-diabetic range in one lab may be more or less than 1 point above the non-diabetic range in another lab.
I think it is important to remember that the Hemoglobin A1C is just a test that gives you an idea of the average blood sugar over the past 2 to 3 months. If measured every 3 months in the same lab, it will tell you whether your average blood sugar is changing, but will not tell you anything about the details of your blood sugar - i.e. is it bouncing up and down, is there any pattern that it is high or low at any particular time of the day, how does exercise effect your blood sugar? Only frequent daily blood sugar monitoring can give you this detailed information and guide you on how to adjust your insulin, diet, and exercise on a day to day basis.
Answer from Dr. Robertson:This is my pet hobby horse. I predict a campaign from patients demanding some consensus on HbA1c methodologies. The present situation is diabolical - in Scotland when we surveyed in 1994 there were more than 10 different methods being used. With patients more interested to know how they compare with DCCT results, this situation is no longer tenable.
Answer from Dr. Quick:I participate in a dozen or more managed care plans that insist that my patients utilize different labs, which have different normal ranges for glycohemoglobins. It's all very frustrating, since the glycohemoglobin is such an important test for us to assess the risk of the patient developing long-term complications of hyperglycemia.
I've wondered how long it will take for the clinical pathologists who run these labs to wake up and smell the coffee, that they're not running the only lab in the world, and that we want standardization! The main pressure to standardize so far, seems to me to be coming from us endocrinologists who have to explain the differing norms to our patients, and the craziness of the different normal ranges: for example, a 7.0 may be "normal" in a lab where the upper limit of normal is 7.8, or "high" if the limit is 6.5.
There're rumors of the beginning of a move in the US to redefine the norms in reference to the DCCT's glyocohemoglobin methodology (which technically is called HPLC for short).
If you, dear reader, as a patient or parent of a patient, have run into problems similar to those mentioned in this question, I'd suggest that you show a copy of this page to your Diabetes Team, and ask your Diabetes Team to pester the Lab Directors to standardize on the HPLC technology! (And let's start a huge campaign to get the normal ranges and methodology standardized!)
Original posting 1 Aug 96
Last Updated: Tuesday April 06, 2010 15:08:50
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