My Meter Readings

[Squire Fulwood]

I haven't received the solution yet, but that wasn't the point. I wanted to know the concentration of the control solution so that when I take readings I can see how far out my meter is.

Yes that's why I asked but if you don't have the control solution yet it will be difficult.

 

[Bellx15]

OK - I'll keep you posted, but I do think there has been a mistake somewhere.

 

[Squire Fulwood]

Each 4.0 ml vial of Abbott FreeStyle glucose control solution contains:- D-Glucose* ( Low 0.05%; High 0.3%), preservative, FD&C red dye, viscosity-adjusting agent.

* D- Glucose is also referred to as dextrose.

I will test my strips later.

These numbers seem very precise. They do not say if there is a tolerance here.

 

[Bellx15]

The tolerances relate to the testing machine's accuracy, so should be on the strips container. The control solution has to be precise.

 

[Squire Fulwood]

0.05 solution equates to 2.8. Permitted range 1.6 to 3.3. Actual reading =2.8

0.3 solution equates to 16.7. Permitted range 13.8 to 20.7. Actual reading = 17.3

The is for the Freestyle Freedom Lite and using test strips from a batch higher than 1258621 and using the amended ranges.

 

[Bellx15]

Your figures make sense - actual solution midway between tolerance limits. Mine don't. I have emailed back to the Roche technicians and I'm awaiting their explanation. Actual solution - 6.7mmol/l, tolerance limits 6.7 - 9.0 ???

 

[Squire Fulwood]

That'll be the last time I make sense today. I have found out where I hid the corkscrew and it's goodnight from me ....soon.

 

[Bellx15]

That'll be the last time I make sense today. I have found out where I hid the corkscrew and it's goodnight from me ....soon.

:lol: :thumbup:

I'll drink to that!

 

[Bellx15]

Could be entertaining though ...

By the way, I'd appreciate an opinion on this:

I haven't done a proper GTT test but for now I thought I'd monitor my response to a light tea. It consisted of three small slices of wholemeal bread, one fried egg, butter, a substantial blob of peanut butter, two glasses of white wine.

Results (probably higher than true readings because of the machine): Before the food - 6.5, 1 hr after the food- 6.8. 1.5 hr after the food - 7.9, 2hr after the food - 7.4

Update: Tried a tea with another full white roll added (one of those dense, Italian type rolls). Now 11.1 after two hours (minus the error introduced by the machine, say 1.0). Have to be careful!

After three hours down to 8.7

 

[Bellx15]

Regarding my meter, I have received and used the control solution now, and I am still confused.

The solution is specified as being 0.12% (by weight) glucose, which I think translates into 6.67 mmol/l.

However, the margin of error allowed for the machine testing the control solution is given as 6.7 - 9.0 mmol/l , which is all above the value I just calculated. It's supposed to be an equal plus/minus tolerance. So according to all that the machine is expected to read about 1.15 mmol/l high.

Where am I going wrong here?

[PS The actual reading for the control solution is 8.1 mmol/l]

 

[Squire Fulwood]

Where am I going wrong here?

Pass.

 

[Bellx15]

Where am I going wrong here?

Pass.

I just called the Roche technical staff, and he said it was the first time anyone had asked him this question (!!!) Most users just check that their control reading falls between the limits (6.7 - 9.00) and that's that.

I said I was fine about that until it occurred to me to wonder what the actual concentration of the solution was. When i looked into it it appeared to be 6.67mmol/l, which seemed further to make no sense. Putting all this together you have to infer that the meter reads around 1.15 mmol/l high. The only possible error in my calculation would be if 0.12% (by weight) for some reason doesn't translate into 6.67 mmol/l.

He's going to check with his mates and email me back.

 

[Bellx15]

0.05 solution equates to 2.8. Permitted range 1.6 to 3.3. Actual reading =2.8

0.3 solution equates to 16.7. Permitted range 13.8 to 20.7. Actual reading = 17.3

These figures you provided support my own calculation, for 0.12% control solution:

0.12 x 2.8 = 6.72 mmol/l
0.05

I can't see any possible way out of this - my machine is known to systematically read over 1.0 high. The acceptable range printed on the test strip box must allow for the systematic error produced by that batch of strips.

But even if that is true, there are no instructions to make allowance for this systematic error when reading your BGs.

I can't wait to see what they say.

 

[Squire Fulwood]

0.05 solution equates to 2.8. Permitted range 1.6 to 3.3. Actual reading =2.8

0.3 solution equates to 16.7. Permitted range 13.8 to 20.7. Actual reading = 17.3

These figures you provided support my own calculation, for 0.12% control solution:

0.12 x 2.8 = 6.72 mmol/l
0.05

I can't see any possible way out of this - my machine is known to systematically read over 1.0 high. The acceptable range printed on the test strip box must allow for the systematic error produced by that batch of strips.

But even if that is true, there are no instructions to make allowance for this systematic error when reading your BGs.

I can't wait to see what they say.

Before this investigation began I knew how to convert mg/dL to mmol/L but I did not know how to convert percentage to mg/dL since I did not know whether it was by volume or by weight or whatever. The reason my calculations support yours is that you said it was by weight and so I used your calculation method.

I now propose a hypothetical situation. Suppose I made blood glucose monitor meters and further suppose that I made one that read high such that there might be a danger of it failing the tolerance tests under some circumstances. What could I do to lessen that possibility.

Well I could publish a tolerance that had the actual concentration of the control fluid at the low end of the tolerance. The meter can then read as high as it likes.

Of course, this is only hypothetical case since I do not wish to make unfounded accusations without being sure of my facts but I think I may know another machine with a similar problem.

 

[Bellx15]

Ok - understood.

But yes, the percentage is given in terms of weight - that is specified. So it follows that % weight divided by molecular weight cancels out the weight unit. What you are left with is a simple numerical value - in mols (mmol/l). That seems to be right.

it might be systematic error by the test strip batch. They know the strips read high, so set their tolerance band accordingly. So yes, I can see that too. Problem then is that nowhere have they mentioned this systematic bias, so when you take your BG readings they will be high but you won't know it.

Conspiracy??

 

[Squire Fulwood]

Conspiracy??

I didn't want to use that word because of the existence of conspiracy theorists and how daft they can look sometimes but I am faced with a couple of facts.

The low end of the tolerance of your machine/strips is 6.7

The control fluid converted to mmol/L is 6.7 (ok 6.67 but my meter only reads to one decimal point.

What am I to make of that? ..........ok, I give in.

 

[Squire Fulwood]

I have another make of meter and there have been many suggestions by people on this forum that meters of the same make read high. I did extensive tests on it and proved that it reads one unit higher than my Freestyle. That's all I could say before now.

Now that I have more detail about the control fluid in my possession I intend to test the other meter again. I have no test strips for it but I have ordered some.

When they arrive I will let you know the result.

 

[Bellx15]

Conspiracy??

I didn't want to use that word because of the existence of conspiracy theorists and how daft they can look sometimes but I am faced with a couple of facts.

The low end of the tolerance of your machine/strips is 6.7

The control fluid converted to mmol/L is 6.7 (ok 6.67 but my meter only reads to one decimal point.

What am I to make of that? ..........ok, I give in.

The only glitch in your theory is that they have left themselves no room for error on the downside. Would they be willing to take that risk? maybe it's just a simple human error, but i find it unbelievable that I should be the first person simply to ask what the control concentration is.

 

[Squire Fulwood]

The only glitch in your theory is that they have left themselves no room for error on the downside.

If I knew that it always reads high I would not have to leave room for error on the downside. I could avail myself of the entire tolerance of -0/+40%.

I agree that something is not right here but your figures are actual figures and this is what they suggest. I am happy that my meter bears out your thinking of using the control fluid solution in this way. This makes me think that you have the method. My low reading was on the nose.

 

[Bellx15]

The only glitch in your theory is that they have left themselves no room for error on the downside.

If I knew that it always reads high I would not have to leave room for error on the downside. I could avail myself of the entire tolerance of -0/+40%.

Not really - as soon as someone like me gets an independent test (from the hospital) they find out that the meter is miles out. Mine was showing 6.7 when the hospital told me it was 5.3 . If that 5.3 falls below a 10% margin from their reading they are in trouble. the point is that although they know the meter always reads high, it mustn't read more than 10% high. The control solution results/ margin throw people off the scent, but they don't alter whatever error is actually occurring.