Problem with Test strips reading high

[Oldvatr]

I use two meters, an SD Codefree (calibrated to Plasma) and an Abbott NEO (calibrated for wholeblood). For 12 months now the Codefree has consitently measured 12% higher than the NEO due to the calibration ranges issue, but they do track each other quite well when averaged. The only time I ever got the NEO to read close to the Codefree, it was a misread.

I have just changed to a new pak of test strips in the NEO, but the Codefree is using the same batch as last week. I have noted today that my readings have jumped by 2 mmol/l/ My weeky average was 5,0 using the old strips, and the last day averaged out to 5.2 Yesterday my NEO gave me results same as the Codefree, and the daily average has jumped to 7.4. but my Codefree average renains much the same as the week before (7.5) So it is definitely the NEO that has changed.

Looking at the error allowance for a reading of 5.0 mmol/l, then the meter could read +/- 0.75 so a worst case tolerance problem could see a jump of 1.5 max but I am registering a jump of 2.2. So my NEO with these new strips is outside the allowed specification.

I am going to go back to Abbott to see if this is a 'known' problem, or a rogue batch. I will report here what they say when I ring on Monday. Last time I had this problem, the Pharmacy refused to replace the batch, and Abbott sent me a calibration fluid, which of course passed since the limits are that vague a Double Decker bus would pass. So I lost £28 that time. This time I am GP funded so I will have to live with the raised bgl for a month, My spreadsheet can be programmed to compensate so its no worry so long as I remember to remove the fiddle factor on next strip change.

 

[lynn007]

I have noticed using to different machines it gives a different reading and also done befor I had my blood taken at the gp that it was 3 different readings , strange really, same finger same blood same time.

 

[Oldvatr]

I have noticed using to different machines it gives a different reading and also done befor I had my blood taken at the gp that it was 3 different readings , strange really, same finger same blood same time.

Repeatability of measurement is always difficult to achieve in practice expecially in a portable meter that is not maintained to laboratory standards. Simple logic says same blood, same meter should equal same result, but the strip has changed, The blood has started to react with contamination on the skin, and has started to change compostition due to oxygen exposure, and congealing Sometimes I need to squeeze my finger to get the second drop, which also will change the blood composition.

The meters will have their own accurcy tolerance, currently +/- 15% of reading so 3 meters in parallel can differ by 30% worst case off the same drop anyway. This is why it is best to use averaged values, and look for trends rather than worry about absolute accuracy of any single timepoint reading. In my posting above, I regard my weekly average as being closer to where I am than the daily average for any given day, since diet and other factors will alter it. So the weekly average between my two meters works out at (7.5 - 5.0 = 2.5) and this is way above the expected 12% ecpected error due to the calibration alone, so this means that either my SD is reading high, and / or my NEO is reading low, so in probability both are out. However, changing strips on one meter should not change by more than the tolerance allowed for that meter and this is definitely wrong.

 

[lynn007]

I never need squeeze my finger much it comes out easy even my cousin said well your a bleeder

 

[Oldvatr]

I had a chat with the nice people at Customer Care at Abbott, but I am more confused than I was before. Firstly, we had communication difficulties with difference in language, which made discussions at a technical level difficult, Then the support guy did not seem too lnowledgeable about the product, so there was often a 3 way conversation with the supervisor.

Initially I was doing it all wrong, The meters give an accurate measurement of blood glucose levels, and that is all. When I asked if the NEO was calibrated for whole blood or plasma equivalenr, I was told they only measure blood glucose levels, and are not calibrated. Why do I ask? Coz it makes a 12% difference in reading thats why.

Then we had a discussion on what I meant by whole blood vs plasma. Apparently it is inpossible for the Abbott meters to read plasma or interstitial fluid, only whole blood. I was told all Abbott meters are whole blood, which I know is not true. the Libre is Plasma Equiv. As is the Freestyle Lite. It says so in the owners manual. But the rep insisted none of their meters can be used to measure plasma. I had their website copy of the LITE owners manual open at the time, and it was quite clear to me that it is scaled for plasma.

Anyway, the rep sent me some test strips to try. They agreed with my latest batch, and are still reading high compared to the batches I have used over the last 9 months. So not resolved.

One problem I now discover is that in reading the leaflet for the new strips, I come across the following description for accuracy assay tests for the strips

The YSI 2300 Stat Plus glucose analyser served as the
comparative method in the clinical and laboratory studies.
The YSI whole blood glucose results were multiplied by 1.12
to obtain plasma equivalent glucose values for comparison
with the test strip results. The YSI glucose analyser has
metrological traceability to NIST certified reference material.

In essence this means that the Freestyle Optium strips give Plasma Equivalent readings. I cannot find my old batch leaflet to see if this is a recent change or not, but it means that the Customer Care guys were wrong. It explains a jump I saw last week, and why my NEO is relating closely to my SD Codefree whereas for the past 9 months it was always 1 or 2 or even 3 mmol lower. Now I get physical symptoms of hypo that start when my meters read 5.5 or lower, not the 3,8 or lower I have been used to. It also means that the 1.5mmol rise in average bgl this week may not be something I have done or not done, but simply my meter playing up.

I have a new batch of strips with different expiry date to try, so will see of this change is a permanent one.

 

[himtoo]

are you taking insulin ?
if so the results can have a big impact on treatment ?

 

[Oldvatr]

are you taking insulin ?
if so the results can have a big impact on treatment ?

No I have avoided insulin so far, but I totally agree with your POV. This is a real problem that has not been resolved, and at the moment the NICE targets seem to remain as whole blood, not plasma.

For me as a T2D on orals and diet, I only have minor problems, and being hypo aware, I do not need to rely on my meter so much. But I wish the manufacturers came clean about how their meters are scaled. and how these relate to the relevant National guidelines. At least Accuchek and SD have made clear declarations for their meters, but Abbott has always hidden this info. I believe TRUE METERS are also Plasma, but only in New Zealand, The Gluco RX is calibrated against any meter, so will align to whatever scaling that meter has. These are the only meters I have managed to get declarations for so far.

 

[Oldvatr]

No I have avoided insulin so far, but I totally agree with your POV. This is a real problem that has not been resolved, and at the moment the NICE targets seem to remain as whole blood, not plasma.

For me as a T2D on orals and diet, I only have minor problems, and being hypo aware, I do not need to rely on my meter so much. But I wish the manufacturers came clean about how their meters are scaled. and how these relate to the relevant National guidelines. At least Accuchek and SD have made clear declarations for their meters, but Abbott has always hidden this info. I believe TRUE METERS are also Plasma, but only in New Zealand, The Gluco RX is calibrated against any meter, so will align to whatever scaling that meter has. These are the only meters I have managed to get declarations for so far.

Just to update on my situation. I have now got sufficient data points to be able to apply serious filtering on my results to remove day-to-day noise and interference,
If I make the original assumption that my NEO is whole blood, and my SD is plasma calibrated, and apply the correction factor to make them both plasma equivalent or vice versa, thn the difference between the two meters is less than 0,5 mmol.l/ The Neo has moved closer to the SD since the test strip change, but only by a small amount. If I remove the compensation for calibration, then the differences show up as around 1.6 mmol/l which is close to the 2 mmol jump I thought I saw. So I was fooled by the meters having different calibrations.

In conclusion, it seems to confirm that the NEO is reading as whole blood, and the SD is plasma. I do have a fixed 12% difference between them.

The new strips have altered the results,and are within the tolerances allowed, but I do need to work with compensated results, not meter screen numbers. Mentally I can drop/subtract my NEo results by 1.6 to get back to where I was.with the old strips/So I am looking at possible hypos when the NEO reads 5.4 or less, which also matches my recent physical symptoms.

 

[Bluetit1802]

Much of the confusion arises because the instruction booklets say only to measure whole blood from a capillary in the finger tips or wherever, and assume the readings are whole blood. People don't tend to read the technical data further on, which will say it is calibrated to change the whole blood reading to plasma blood (or not, as the case may be). It is likely the Abbott staff you spoke to were such people.

 

[Oldvatr]

Much of the confusion arises because the instruction booklets say only to measure whole blood from a capillary in the finger tips or wherever, and assume the readings are whole blood. People don't tend to read the technical data further on, which will say it is calibrated to change the whole blood reading to plasma blood (or not, as the case may be). It is likely the Abbott staff you spoke to were such people.

I have checked the Abbott Users manuals, and the only ond that gives any declation is the Freedom Lite. My NEO and my EXCEED leaflets fo not mention it, and the description I copied from the Optium test strips (in my previous posting) is the closest they come to it, but they do not declare it anywhere in the manuals or on their website.

SD have a clear statement in the tech spec section.

The Accuchek leaflets do not state it, but there is a notification on their website.

The Libre does not declare it in the Abbott literature I have seen (it just says the meter is factory calibrated), but there is a test report / review report that mentions it being plasma equivalent. I have also viewed the Freestyle literature for the Australia market.

Edit to add: apparently Verio One Touch is plasma equivalent.