HbA1c POC Testing
Hello,
Has there been previous discussion regarding the accuracy of POC HbA1c testing and how it correlates with the lab? We are currently using the DCA Vantage in our physician offices.
I have a doc who is concerned about variation in POC HbA1c testing and samples that are sent to the lab. I just recently came into this role so I do not have much background information regarding the concern. By what I have collected so far, there have only been a few patients that have shown a higher POC A1c result than what was performed in the lab. The variation has ranged from 0.4-1.0%. I do know that due to different sample types (POC-capillary and lab analyzer-venous) that there is an expected/allowable amount of variation in results. I informed the doc of this, as well as variation in POC operator technique (which I plan to assess to see if it is contributing to the variation in results). I respect the doc's concern but with a lack of data and so many other variables I am hesitant to jump to the conclusion that the variation is coming SOLELY from the POC instrument.
Has there been anyone else out there that has shown concern regarding the lack of correlation between POC HbA1c testing compared to the lab analyzer?
Thanks in advance for your help! :)
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When we put our DCA Vantages into place a few years ago our validation studies showed a bias between the POC analyzers and the Lab (+/- 0.3). We made that known
to the providers and cautioned them to only trend on one analyzer and not to jump back and forth as that would just confuse things.
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Raychel,
Start with looking at your Proficiency Testing results to compare the DCA peer group average and range against that of the main lab's peer group. Do you have different reference ranges established for each of the two reporting methods?
Different methodologies (agglutination, cation exchange, immunoassay, affinity chromatography) would/should most likely have their own reference ranges. The greatest disparity would naturally occur at the higher ends of reportable ranges which is what you are indicating.
Education may be the most appropriate plan, assuming your research is substantiated.
Please also considering referring to the attached files CAP from NGSP showing the different methodologies and differences in results using the same testing materials.
See also the Interferences with GHB when testing for HbA1c.
I've been also told, by PhD's that each methodology may have different Normal Ranges for these various devices and this also must be taken into consideration when comparing results with different HbA1c methods and instruments.
When you said you had a 0.3% variation, this is normal when taking the above and attached into consideration.
Bottom line, if controls are consistent and accurate on the DCA Vantage, then this is usually the POC measurement the clinicians will use to successfully manage their patients with diabetes.
Raychel,
We evaluated the DCA Vantage about 6 years ago (but never implemented, for different reasons), but it compared very well. No bias, and no variation greater than 0.4 from an outside reference lab. Here is our data (note: these are all EDTA tube samples, I believe):
It's been a long time, but one thing I do seem to remember about the Vantage is there is a timing limit between sampling and testing? If I had to guess, I would be suspicious that staff may be pushing the limit on how long between sampling and testing.
Good luck!
Actually, the Siemens DCA Vantage A1c has the longest lag time from capturing the patients fingerstick or vacutainer whole blood sample; 5 minutes.
Here is a study done a while back on POC HgbA1C instruments available in the market at the time.
DCA Vantage and Afinion got thumbs up.
There could be newer ones that came up since but I have not seen another study.
Pet Maniquis, MPA, MT(ASCP) POCS (AACC)
Laboratory Point-of Care Coordinator
Providence Medical Center/ Saint John Hospital
8929 Parallel Parkway, Kansas City, KS 66112
Ph: 913-596-4727; Fax: 913-596-4728
PManiquis@primehealthcare.com
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Does anyone have info on the A1CNow + by PTS Diagnostics? Its a kit that comes with a reader and cartridges which are coded to work together. The readers are thrown away with each kit and a new one is put in use when opening the next kit. I think there's a home version but this one is made for professional use.
We evaluated the A1CNow+ last year. In general, for patients with A1c <6.5% the meter gave falsely elevated results, and for patients with A1c >6.5 the meter gave falsely low results. Results from this device would have misclassified 15% of our test subjects. Precision was 4.3 %CV.
The package insert lists interference from hemoglobin F, S, C, or "other hemoglobin variants" and from "high amounts" of rheumatoid factor.
The meter was little tricky to use, and you have to be careful not to drop any of the components (meter, test cartridge, blood collector, sampler) because they come as a set.