September 13, 2007
A1c (Glycohemoglobin, HgbA1c)
Question from Cologne, Germany:
Since moving from the U.S. to Germany about a year ago, my A1cs have consistently been much higher, even though my meter averages have gone down. I’m on a pump, test eight to 10 times per day, including overnight, and my meter numbers have always matched my A1cs very closely, until now. I recently discovered that, although the treatment goals are exactly the same in both countries (below 7.0% and below 6.5%, ideally), the Germans seem to use a very different laboratory assay. In most U.S. laboratories and nearly all medical web sites I can find, an average blood sugar of 135 mg/dl [7.5 mmol/L] should correspond to an approximate 6.0 A1c. However, in Germany that same average is said to be a 6.5 A1c! Consequently, for each blood sugar average, one’s A1c will look at least half of a percent higher here. I know laboratories can be different, but my doctor said this is the standardized German laboratory assay and, of course, the most accurate one possible. Are you aware of such a big difference between American and European A1c standards? As I said, the treatment goals are still the same. In the end, it means that U.S. doctors want us to average 152 mg/dl [8.4 mmol/L](6.5%) or less to avoid complications, but one must be at 136 mg/dl [7.5 mmol/L] or less in Germany to achieve the same result. How can that be?
Answer:
You bring up a very important point on which many people have been working. There is a lack of standardization for HbA1c assays. It is possible that they are using a total glycosylated hemoglobin assay, not a HbA1c. HbA1c is a significant majority of the total glycosylated hemoglobin, but the total glycosylated hemoglobin is always higher. Additionally, the vendors for German laboratories may not use commercial assays that have been normalized to the American standards. This has been done by selling a product where the result has been standardized to a level that was performed by a method used in the DCCT. The DCCT was a large North American trial that clearly showed that control mattered. The HbA1c levels were measured by HPLC (high performance liquid chromotrography). This may not be done in Germany. Soon, there are plans to make the HbA1c universally standardized using a different set of numbers so this area is in flux for the moment. You may want to have simultaneous values obtained from your local physician and through an American assay, maybe one done at the hospital in Frankfurt on the air base or sent to an American reference laboratory. It is an important clinical question because you want to know if your control is worsening or if it is really the same and related to technical issues.
JTL
