Testing the Tests of A1C
Bayer Diabetes Care's A1CNow+ monitor for us to test our A1C level at home carries the highest certificate of accuracy. As I wrote here in June, the NGSP (formerly the National Glycohemoglobin Standardization Program) certified this device as having documented traceability to the Diabetes Control and Complications Trial reference method, which established relationships between A1C levels and risk for complications of diabetes. The DCCT method is the gold standard for reliable A1C testing.
So I was surprised to read an article in the journal Clinical Chemistry indicating that this was one of the A1C testing devices that didn't meet "the general accepted analytical performance criteria." Two Dutch researchers led by Erna Lenters-Westra reported that the local distributor in the Netherlands of the A1CNow+ Bayer "concluded that the EP-10 [protocol] outcome data did not warrant progression" to the two other protocols the study used.
But the key sentence -- buried in the full-text of the study and missing from the online abstract -- is this, "The bias found with the EP-10 protocol of the A1CNow was probably due to EDTA interference problems."
I had to ask Bayer representatives what all this means. This is what the company told me:
"Bayer has reviewed the Lenters-Westra study published in Clinical Chemistry that used Bayer Diabetes Care's A1CNow+® monitor as part of their evaluation," the company wrote back. "Bayer believes that the results that the study authors obtained did not accurately capture the proven performance of the A1CNow+ device due to use outside the manufacturer's specifications [emphasis added].
"The A1CNow+ Product Insert states that A1CNow+ may be used with either fingerstick (capillary) or venous (heparin-anticoagulated) whole blood samples. When used according to the product insert, the results showed that the accuracy of A1CNow+ with fingerstick samples was, on average, 99%. The results showed that accuracy with venous sampling was, on average, 99.7%. Utilizing other anticoagulants, such as EDTA, with the A1CNow+ device will often result in a negative bias, thus affecting the accuracy of the A1C results obtained [emphasis added]. According to the Clinical Chemistry article, the Lenters-Westra study used EDTA anticoagulant."
This shows to me that studies are not always what they seem to be on the surface and that we shouldn't jump to conclusions when we have only the abstract of a study. None of the other A1C testing devices that the study evaluated are available for home use, although a few mail-in kits that the study did not evaluate are on the market. The A1CNow+ remains my favorite.
Update February 3, 2010:
I wrote the lead author of the study. This is her reply:
"Thank you sending me the response from Bayer.
"We haven't been in contact with Bayer in the past only with the local distributor (Euromedix). Euromedix had no comments on our study protocol and they didn't informed us about possible interference with EDTA. The product insert is not very clear about the use of EDTA. They also didn't want us to continue with the evaluation because of a large bias (probably due to EDTA) and high CV (no explanation). We offered them to investigate this with capillary blood but they were not willing. We also advised Bayer to carefully check and educate their local distributors.
"At this moment we are trying to convince Bayer to do a new study study on condition that whatever the outcome will be, we will do our very best to get it published. We are currently waiting for their answer.
"The only reason for us to do this evaluation is for the patient. Not for ourselves, not for the manufacturer, only for the benefit of the patient."