Accuracy of monitoring

[Yorksman]

Looking into the accuracy of the results in self monitoring, I came across this study, 'Factors Affecting Blood Glucose Monitoring: Sources of Errors in Measurement', http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2769960/ Apologies if it has been posted before.

Results can be affected by many factors:

"Glucose monitoring has become an integral part of diabetes care but has some limitations in accuracy. Accuracy may be limited due to strip manufacturing variances, strip storage, and aging. They may also be due to limitations on the environment such as temperature or altitude or to patient factors such as improper coding, incorrect hand washing, altered hematocrit, or naturally occurring interfering substances. Finally, exogenous interfering substances may contribute errors to the system evaluation of blood glucose."

Not a single reading may be representative. It's the averages that count. You can see this in fig. 1 http://www.ncbi.nlm.nih.gov/pmc/article ... gure/fig1/ As the text explains, "the average of a series of values can be perfectly accurate, although none of the individual values is representative of the reference."

Most importantly is the accuracy of the meter itself. The ISO 15197 standard calls for a minimum accuracy of ninety five percent of all measured values to fall within:

20% of glucose values above 75 mg/dl
15 mg of glucose values below 75 mg/dl

In other words, if for the upper range the true value would be 7.0 mmol/L, the meter is deemed accurate if it reports 95% of the time anything between 6.3 mmol/L and 7.7 mmol/L. For the lower range, anything below 4.1 mmol/L is deemed accurate if it is plus or minus 1.0 mmol/L

Now, take that upper range 6.3 to 7.7 which represents meter accuracy and then add strip accuracy, which can vary depending on how it has been stored and the testing environment, which can vary on the temperature and then the accuracy of the blood sample, which can can vary depending on what one has squeezed out of the puncture and also on what contaminants are around, and you have a a lot of reasons to be suspicious about the accuracy of the individual reading. All these factors vary however and tend to level each other out. So, do not get phased by individul readings and keep a record, most meters to anyway, of your averages.

 

[donnellysdogs]

Well to add to confusion..

My hba1c from my arm at gp came in at 7.2 (55).
Was pleased with that.. Consultant wanted it nearer to 8.0.

Saw consultant today. 6min finger hba1c... 6.5!!

So which one is believable?

 

[Squire Fulwood]

I like this reply from Roche. It makes my eyeballs dry out.

Thank you for contacting Accu-Chek.

Please be aware that performing a control test in your home environment cannot by compared to performing a control test in a laboratory, as the strict laboratory testing conditions are not met in the home environment. This means that achieving the target reading of 6.67 mmol/l is not possible. Due to these factors a target range has instead been calculated. This range takes into consideration the effects of temperature deviations and possible sources of contamination. The specific target range for the Accu-Chek Compact Plus control solution is printed on the peel-off label attached to the drum container.

Please see below important information about performing the control solution test:

Treating the control solution properly:
The solution is filled into the bottle under microbiologically controlled (low germ) conditions. To avoid contaminating the solution, do not touch the tip of the bottle with your fingers, the test strips or the surface onto which you apply the control solution. Contaminated control solution can produce incorrect results.
Use only control solution that is within its expiry date. Expired control solution can produce incorrect results. The expiry date is printed on the bottle.
Store the control solution between +2 and +30°C. Control solution that is stored outside this range may become unusable before it reaches its expiry date.
If you store and handle the control solution properly, it will remain stable for 2 months after opening. However, do not use control solution that is past its expiry date, which is printed on the bottle.
The control solution must be at the ambient temperature when you perform a control test. If you keep the control solution in a refrigerator, leave it to stand at ambient temperature before you perform a control test. Cold control solution can produce incorrect results.

Please also note:
Reproducibility (day-to-day imprecision)
The mean imprecision is < 2%. In a typical series of tests a standard deviation of 0.15 mmol/l was obtained with a glucose concentration of 8.6 mmol/l.
Calibration
The system (meter and test strips) is calibrated with venous blood containing various glucose concentrations. The reference values are obtained using the hexokinase method. This reference method is traceable to a NIST standard by means of the ID-GCMS method, the method with the highest metrological quality.


If you have any further questions please do not hesitate to contact us.

Kind regards,