# Blood plasma readings from testing meters



## Liz! (Feb 8, 2011)

Dear pumpers, I am wondering how many people know about this. 

Some time ago, my Accu-chek Aviva strips changed from giving a reading from whole blood to giving a reading from plasma. I read the insert, and naively assumed that the meter just read the plasma not the whole blood and gave a reading which i would recognise as normal.

However I am a brittle diabetic and my readings and control have been upset for some time. 

I have recently found out that in fact all blood glucose meters now give readings for glucose in plasma, NOT whole blood. Although in fact because you put whole blood in, it tests whole blood and CONVERTS the reading to what it would be if it was testing plasma. 

This means the reading is HIGHER than i am used to. Higher than I have been used to for 30 years.  My nurse told me it was 10% higher, but I recently phoned Accu-chek and was told that in fact it was more like 12.5% higher. But reading around the internet, I read info given to Australian diabetics and they are told it can be anything up to 15% higher. 

Now I exist with very small changes to both my insulin and food levels. A blood sugar of 5 before a meal would mean I gave my normal amount of insulin. but I would hesitate to give a normal amount if my blood sugar was only 4.1 - 4.5, which it might be with this new system. What is more, at the upper end, my pump gives me an extra bolus of insulin in correction after my
blood sugar has reached 16. With a plasma reading my blood sugar could show 17, i might give the correction plus extra, and not realise my blood sugar had not reached 16 at all. 

So - Roche said they'd send a conversion chart. They sent me a new blood testing machine (thank you) but no conversion chart. Have you ever tried calculating percentages in the middle of the night or whilst your blood sugar is low? 

And what is more. I don't want to have to convert or cary a chart around with me! I know where i am - or used to - below 4 i was too low and above 10 -12 I did something about it if not after a meal. 

Why have they done this? Because hospitals use blood plasma readings not whole blood. How does that impact on me? I don't have my blood sugar tested through the day by the hospital. If this has been done for the hospital's convenience, instead of patients' best interests, what does that say about what they care about?

i am so mad about this.


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## Robster65 (Feb 8, 2011)

Hi Liz.

I've no idea why they use plasma readings but there are such great tolerances on the readings anyway, would that not have a greater impact on your control ?

If your meter shows 5, no matter what it is based on, it could still be in the low 4s. The plasma effect may exacerbate that but home meters have never been much used for a truly accurate test. 

Rob


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## Liz! (Feb 8, 2011)

So - I have to judge based on a reading that COULD be 15% higher PLUS a tolerance of 10% even higher or lower? Why change things for the worse?

Actually I have found that my blood testing machines, the Roche ones, have all been very accurate. And consistent. Other machines have not. I've been testing for 30 years and have come to know when a machine is not accurate, and I stop using it.


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## shiv (Feb 8, 2011)

Also bear in mind that BG meters by law are allowed to be inaccurate by up to 20%. So a reading of 5 could in fact be 4 or 6.


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## Liz! (Feb 8, 2011)

But being 'allowed' to be inaccurate and being inaccurate are completely different things. I have had inaccurate meters, but it's very easy to tell. And besides which, a meter would be consistently inaccurate wouldn't it? Probably more so at oe end of the scale. You'd soon know about it. Or i would if my machinge was saying 6 and I found it hard to concentrate 15 minutes later!


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## shiv (Feb 8, 2011)

But it explains why, for example the other night I tested and got 23.5, so retested and got 19.something. It's a big enough difference for me to need a different correction amount, which is obviously important as if I corrected the 23.5 and was actually more like the 19.0, I'm going to end up hypo. 

I don't mean inaccurate as in spitting out totally incorrect readings - they are just allowed to vary the numbers as apparently (and I'm paraphrasing here) 'the majority of people using testing kits are type 2, and it's less important for a person with type 2 to have accurate readings'.


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## Robster65 (Feb 8, 2011)

Bear in mind, also, different fingers can give different readings at the same instant. There are as many variables affecting the result as there are affecting the BG itself !  (well, almost).

For something that we are supposed to be basing our live-preserving medication on, they aren't very impressive. They are, however, all we have for the time being.

Rob


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## Liz! (Feb 8, 2011)

The majority of people using testing kits are type 2? Where do you get that from? That makes no sense at all.

Type 2s didn't use dto be able to get blood testing strips at all. Now it is more common. they are VITAL for type 1s. That is no reason for the numbers to be 'allowed' to be inaccurate. Where did you read this?

I often do tests again, and virtually never get a different reading. I am very used to doing it accurately and of course the meters do depend upon it being done correctly - no squeezing of the finger etc. Diferent places are less accurate than others, the fingertips being best.

Of course you can get get differing readings form different fingers, but certainy not 20% different, the most different I have got are in the point twos!


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## shiv (Feb 8, 2011)

Liz - it wasn't me who said it, lol! When the FDA announced that they deemed it acceptable for meters to vary by law, that was what they stated. Let me go and find the link.

This is a pretty good blog someone wrote covering it. About half way down there's quotes about the need for accuracy with type 1/2.

I only brought it up as I thought it was relevant when discussing accuracies!


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## Robster65 (Feb 8, 2011)

Bear in mind also that the biggest market by far is the US where access to meters and strips is probably very different to the UK. There are a whole lot more T2s than T1s, so maybe they should do a more accurate version just for T1s that costs a little bit more but gives better control. Having said that, for most T1s they are probably close enough for day to day living. 

Rob


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## Liz! (Feb 8, 2011)

They have been in the past Rob. You seem to be misunderstanding what i am saying. I am saying that people don't KNOW that these new machines are giving higher readings CONSISTENTLY than they would have had in the past. 

If your machine that you are using one day, and are used to the readings on, suddenly the next day reads 15% higher, would you want to know? I would.

I know my meter was accurate, and what i was doing was working on the whole, consistently and logically. Since the changeover, things are not the same.


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## Robster65 (Feb 8, 2011)

It's something I've personally considered in the past but only discovered the scale of the tolerance after I joined the forum. It has been discussed a few times on here.
I've been using a BG meter for probably getting on for 23 years, so like you, I've got pretty used to acting on the results. I assumed there was a slightly better tolerance (say 10%) but never thought of it as a constant innacuracy or anywhere near as good as a lab result. As Shiv quoted, for most T2s, which pay the bills of the meter manufacturers, they are probably close enough to make no real difference. 

I know when I'm feeling a bit low or a bit high most of the time and use the meter as a confirmation or to see if I'm somewhere within range. It doesn't matter to me if I'm 5 or 6, but obviously for you it is improtant. If there is a meter that is way more accurate than the others, it would be good for you to have access to it.

Rob

ps. the older machines were no more accurate, they just based readings on whole blood. Inaccuracies will always be there.


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## randomange (Feb 8, 2011)

This might seem like a bit of a naive question, but can't you shift your targets up to take into account the higher readings?

So, for example, tell your pump to correct above 16 instead of 17, and set 5 as your low target?

I understand this won't change the fact that the meter is now reading 12.5 % higher, but it might help you adjust to the new readings without needing to carry around a chart or a calculator!


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## Liz! (Feb 8, 2011)

i know the old machines were no more accurate, but certinly my machine was accurate enough.

That's my point randomange (I always misread your name as random rage!!) I have been trsting too long to adjust. I'm 52, and have been testing since was 22, with the very first meter available. 

To me, 4 is low. I can tell my pump that - but I know where I am at 7. And 10. and 3. And 5... I know what i must do and how to react to all of theses blood sugars at different times of the day and in different situations. It's too late to readjust and work out what to do at the higher reading, and that would also mean looking at the conversion chart.


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## HelenM (Feb 8, 2011)

Liz has a point, but I don't think you can necessarily blame the manufacturers, nor can you blame DUK who flagged up the change for sometime on the website. You can, perhaps, blame the health care providers for not giving  enough info though they probably don't want to  confuse.
 .
 When I was first diagnosed (in France) I was given an accuchek meter (whole blood) and told that the hospital preferred this meter.  All the info sheets were based on readings from that meter.The figure for a hypo was   less than 60mgdl, (3.48mmol). I wondered for a while why this was so much lower than in the UK, now I think it was perhaps to take into account that it was a whole blood reading. 60mg/dl on a whole blood meter is about 67(3.7mmol) on a plasma one.
When I changed to a plasma calibrated one touch  I  changed to using  70mg/dl (3.88mmol) which is the level people in the US also use.(they have had all plasma meters for many years)  My pump settings are now based on plasma readings.


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## Ellie Jones (Feb 9, 2011)

I never quite get the plasma debate at all...

Even for T1's it's not a major issue at normal levels the differential isn't going to make a major difference even at 15%, it's only really slightly more problematic at higher levels..  But easily resolved by a slight regig in correction factors, which is somthing that we all face over a period of time anyway...   

As our insulin needs naturally change over the years as we get older fact of life...

I actually only use one meter for testing, the spare meter I have is only ever brought in for emergencies i.e if my main meter breaks...   As using several different meters to monitor you control can have a bigger impact on control than the tollerance or plasma reading can...

But you can get a good gest if your meter is reading high, by looking at your results and comparing to your HbA1c..  I remember dumping one meter because I was getting what I thought very nice bg's but when the HbA1c's told a different story, I double checked it with a different meter which read higher, so changed to this meter and got a lot better result the next time..

Now every time I have to use get a new spare meter, I double check the results with the current one over several tests to see how it reads, I take note of this so that if I've got to bring it in use, I can make any necessary adjustments to my targets to maintain good levels..


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## Alan S (Feb 9, 2011)

Liz! said:


> The majority of people using testing kits are type 2? Where do you get that from? That makes no sense at all.


Actually, in countries outside the UK where strips are not so tightly restricted, that is quite true. Yes, most type 2s test less often individually than type 1s but the T2s outnumber T1s by about 20 to 1. Similarly, more insulin is used by T2s around the world than by T1. There are more T2s using it and they generally use much higher doses because of their insulin resistance.

Getting back to plasma versus whole blood, the differnce is approximately 11%. That equates to approximately 0.5 mmol for a reading in the 5s and 1 mmol for a reading in the 10s. My average rose about 0.5 when Accu-chek changed the strips here.

Most meters are lucky to be within 5-10% anyway. If you get a meter that is within 5% for repeatability you are doing well. The world appears to be going plasma, so we'd better get used to it.


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## Liz! (Feb 9, 2011)

I was told 11%, but phoned to check and Accu-chek told me themselves it is actually 12.5%. 

It maybe no probelm to those whose control is easy, but for me it's real pain.


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## Ellie Jones (Feb 9, 2011)

Liz

I can't see why it's a big problem for you..

As it seems a pretty easy one to reslove...

Just change your correction factors to suit the new readings!

The new plasma reading will be constantly around 12.5% higher!  If you are using a bolus wizard on your pump, you just change the correction ratio to reflect this factor...


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