Plasma/whole blood testing & measurement

candyfloss · Oct 21, 2009

I did wonder about breaking this up into more than 1 topic - and if I should use the soapbox but anyway here goes...

The Americans (& I dont know who else) measure mg to ml when analysing blood. Can anyone (American or otherwise) explain to me the scientific argument for measuring weight to volume??
It makes sense to me to measure like with like, e.g. volume in a volume or weight in a weight. Why did they chose mg/ml (or we mmol/l)?

I read somewhere that in a Lab setting blood glucose is measured from plasma not whole blood and that tests on plasma will be overstated by 12% given the same sample of whole blood. Correct?
I assume all Hb1Ac tests (and other lipid profile tests?) are done in a Lab and presumably these will use PLASMA. Correct?

On American web sites I see cholesterol and tryglycerides often quoted in higher figures. Is this again likely to be mg/ml?? So to convert to mmol/l - divide by 18??.... same for tryglycerides??

phoenix · Oct 21, 2009

candyfloss said:
I did wonder about breaking this up into more than 1 topic - and if I should use the soapbox but anyway here goes...

The Americans (& I dont know who else) measure mg to ml when analysing blood. Can anyone (American or otherwise) explain to me the scientific argument for measuring weight to volume??
It makes sense to me to measure like with like, e.g. volume in a volume or weight in a weight. Why did they chose mg/ml (or we mmol/l)?
No idea of the history behind it

I read somewhere that in a Lab setting blood glucose is measured from plasma not whole blood and that tests on plasma will be overstated by 12% given the same sample of whole blood. Correct?
I assume all Hb1Ac tests (and other lipid profile tests?) are done in a Lab and presumably these will use PLASMA. Correct?
Lab tests use plasma,
All monitors use whole blood but many then 'correct the figure to plasma.
There is a document listing meters in the UK and whether they read in plasma or whole blood (slightly out of date)
'A guide to whole blood and plasma calibrated blood glucose meters on the UK market.'
(sorry, you'll need to google, I've just updated adobe reader and it seems to work differently, I haven't worked out how to link from documents)
Figures quoted in offical documents such as NICE refer to plasma.
Some people on these forums will use meters giving whole blood readings, others plasma converted, we may not be comparing like with like . All US monitors give plasma readings.

On American web sites I see cholesterol and tryglycerides often quoted in higher figures. Is this again likely to be mg/ml?? So to convert to mmol/l - divide by 18??.... same for tryglycerides
to convert mg/dl of total cholesterol, HDL or LDL cholesterol to mmol/l, divide by 39 (or multiply by 0 .026)
to convert mg/dl of triglycerides to mmol/l, divide by 89 or( multipy by 0.011)
All substances differ.
http://www.vin.com/scripts/labquest/converthtml.pl

candyfloss · Oct 21, 2009

Thanks - useful to have the numbers to convert to mmol/l

hanadr · Oct 21, 2009

Oddly, since they haven't a clue about it, the only units that have any legal standing in the USA are metric.
Using mg per decimetre cube is a simple way of expressing a solution. It's mass of solute in volume of solution.
the mole is actually quite useful when considering chemical reactions.and it gives geeks like me something to write about 8) . A molar solution contains the Relative Molecular Masss in grams of the substance in 1000 centimetres cubed of solution. It's useful when considering chemical reactions.
One mole of sodium reacts with one mole of chlorine to form one mole of sodium chloride, irrespective of how much water is present.. Make it up to 1000 cubic centimetres of solution in pure water at 20 degrees Celsius and standard atmospheric pressure and you have a molar solution. A millimole is diluted to 1/1000 of that.
Germany uses mg. The conversion factor is 18, because theRelative Molecular Mass of glucose is 180
Each conversion factor depends on the Relative Molecular Mass of the molecules.

candyfloss · Oct 22, 2009

thanks Hanadr

although its very technical I like to get a little bit of the scientific background to all of this.

so basically the meters we use at home take the measurement in whole blood but are programmed to display the plasma equivalent which is 12% higher. Thus no need to make any further calculations/adjustments when we are given the results of a lab test.

Sid Bonkers · Oct 22, 2009

hanadr said:
the mole is actually quite useful when considering chemical reactions.and it gives geeks like me something to write about 8) . A molar solution contains the Relative Molecular Masss in grams of the substance in 1000 centimetres cubed of solution. It's useful when considering chemical reactions.

Does Secret Squirrel know about this Hanna?

phoenix · Oct 22, 2009

no, not all In the UK, It depends on the make.
Abott: Optimum, precision , exceed... plasma calibrated
Bayer Acensia , whole blood calibarated
DiagnoSysMedical TrueTrack... plasma calibrated
Lifescan One touch Ultra, Ultra Smart...plasma calibrated
Menarini Diagnostics GlucoMen PC...plasma calibrated
Roche Accuchek, Advantage, Avia, Active, Compact plus... wholeblood calibrated
Any others you'll have to check in the instructions

herisson · Feb 8, 2010

Diagnosed a week ago and reading all I can,I came across this discussion on meters. Mine is a Accuchek Aviva and the bumpf says it reads in plasma and it goes on to say that "If you've previously used test strips that delivered blood glucose concentrations on whole blood please note that your meter now displays results that are approximately 11% higher. Accu-chek Aviva Test Strips in your country (U.K.)previously delivered results which referred to whole blood. "
The information from Yorkshirediabetes.com is obviously outdated.I followed Phoenix's link and was very confused by the info. on meters and also anxious that my whole blood readings should be so high.As I've said I double checked with the meter info.and it was as I've set out above.
Therefore,anyone who is using a new Aviva meter will have his or her readings in plasma. If there is uncertainty when the changeover came.the information sheet with the test strips will make it clear under 'Understanding your test results.'
Cheers
Herisson

phoenix · Feb 8, 2010

Herisson, sorry if you were confused. Since the original post Accuchek have changed.
This is from Diabetes UK (the charity)

Roche is in the process of adjusting their meters to give results as plasma values, which they hope will be completed before the end of 2009.

They have obviously kept to their target. Of course the change is to the strips not the meter.
Strangely I've not read anyone saying that their meter is now reading higher !
At least now all meters in the UK are plasma calibrated.

mbkafil52 · Nov 4, 2015

Even after reading all the comments, I still remain confused whether my Accucheck Active meter which previously used strips for whole blood samples and now is supplied with strips that use plasma blood samples is giving about 11% higher results or not. In simple words, do I have to subtract 11% from the displayed reading to get the correct result?

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