About Joslin | Contact Us | Locations | Clinical Studies | Business Partnerships

Plasma glucose ( glucose meter versus lab values )

rated by 0 users
Answered (Verified) This post has 1 verified answer | 6 Replies | 1 Follower

Top 150 Contributor
Female
3 Posts
Sierra posted on Tue, Sep 22 2009 6:44 AM

Hi Everyone,

I am wondering anyone can explain to me on this plasma glucose issue. The newer glucose meters in the market  are all calibrated to read plasma glucose ( capillary ).

And the whole blood calibrated meters are slowly becoming obsolete as they are less accurate - 10-12% lower than the plasma glucose ( lab values - venous plasma).

Is there a variance between the glucose meter plasma glucose values and the lab's venous plasma? Or is it the same irrelevant which plasma glucose ( capillary/venous).

TQ and have a pleasant day!

 

 

 

Answered (Verified) Verified Answer

Top 10 Contributor
Male
378 Posts
Reply
Answered (Verified) Ron AKA replied on Tue, Sep 22 2009 9:49 AM
Verified by zrebiec

A bit of history. In the labs they take out everything but the plasma before they measure the amount of glucose. They don't take the glucose out of course and since the total volume goes down (the denominator), the concentration of glucose goes up. Think of it as a cup of whole blood with say 100 for blood glucose in the cup. You take out 12% of the solids leaving only plasma and glucose. The volume in the cup goes down by 12% and the concentration of glucose goes up by 12%.

It is not practical of course to separate out the plasma from the whole blood at home. For that reason all home meters even the new ones read whole blood percentages. The early BG meters were not sophisticated enough to convert the amount in whole blood measured to a plasma reading so they just read out the glucose in whole blood, and you had to convert that reading to compare it to a lab plasma reading. It is unfortunate that manufacturers choose to display whole blood BG as it causes a lot of confusion when it comes time to compare to the lab results. I don't think it is accuracy between the two types (providing you convert) that is causing the change to plasma calibrated meters, it is simply to eliminate the confusion.

As far as accuracy of home meters compared to lab tests, some are better than others, and most manufacturers rate their accuracy at + or - 20%. There is no doubt that the lab test is more accurate. However on average home meters should be reading about the same. One souce of error in home meters is possible when the amount of solids in the blood are not 12%. If that varies this will cause a small error, but I suspect this is quite insignificant. Just to check my meter I sometimes take three readings with my home meter right after the lab test. I average them and compare it to the lab result when it comes back.

Hope that helps some,

 

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, indapamide, Crestor, & ASA. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

All Replies

Top 10 Contributor
Male
378 Posts
Reply
Answered (Verified) Ron AKA replied on Tue, Sep 22 2009 9:49 AM
Verified by zrebiec

A bit of history. In the labs they take out everything but the plasma before they measure the amount of glucose. They don't take the glucose out of course and since the total volume goes down (the denominator), the concentration of glucose goes up. Think of it as a cup of whole blood with say 100 for blood glucose in the cup. You take out 12% of the solids leaving only plasma and glucose. The volume in the cup goes down by 12% and the concentration of glucose goes up by 12%.

It is not practical of course to separate out the plasma from the whole blood at home. For that reason all home meters even the new ones read whole blood percentages. The early BG meters were not sophisticated enough to convert the amount in whole blood measured to a plasma reading so they just read out the glucose in whole blood, and you had to convert that reading to compare it to a lab plasma reading. It is unfortunate that manufacturers choose to display whole blood BG as it causes a lot of confusion when it comes time to compare to the lab results. I don't think it is accuracy between the two types (providing you convert) that is causing the change to plasma calibrated meters, it is simply to eliminate the confusion.

As far as accuracy of home meters compared to lab tests, some are better than others, and most manufacturers rate their accuracy at + or - 20%. There is no doubt that the lab test is more accurate. However on average home meters should be reading about the same. One souce of error in home meters is possible when the amount of solids in the blood are not 12%. If that varies this will cause a small error, but I suspect this is quite insignificant. Just to check my meter I sometimes take three readings with my home meter right after the lab test. I average them and compare it to the lab result when it comes back.

Hope that helps some,

 

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, indapamide, Crestor, & ASA. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

Top 25 Contributor
91 Posts
Reply
Madman replied on Tue, Sep 22 2009 10:07 AM

exccellent explanation Ron.

I'd like to add though, that 12% is probably not a large enough variance to matter too much.  If the Plasma BG is 100 mg/dl, then 12% would only be 12 mg/dl.  At 200 mg/dl Plasma, the variance is only 24 mg/dl.  Neither of these variances is enough to cause much concern. 

It could be a bit of an issue at lower levels, say 60 mg/dl Plasma, the variance would be 7 mg/dl, but in reality, one should probably already be doing something to treat by the time the BG gets that low anyway.

Top 10 Contributor
Female
229 Posts
Reply
jen1229 replied on Tue, Sep 22 2009 7:27 PM

one should probably already be doing something to treat by the time the BG gets that low anyway.

Well, one should, but one's brain doesn't always function properly when BG is that low. 

I woke up this morning at 2:30 AM and was hungry.  it was much too early to eath breakfast and I had a Dr. Appt hich should have been fasting and I only felt hungry.  I checked BS and it was 62.  In my tired, hungry mind I didn't want to eat that early, so I went back to sleep.  Woke up again at 3:00 AM, still hungry no other symptoms, BG was now 52.  After a few minutes I decided I would eat breakfast and by the time it was ready BG was up to 135.  I ate half of my breakfast when I fell asleep at the table. Woke up BG was 142, finished breakfast,, fell asleep again and when I woke up, because I had taken no insulin I was 234.

I told the doctor what happened and he said to decrease my levimire a couple of units even though my morning numbers are now within range.  Probably a combination of less insulin resistance and the increased exercise along with weight loss.  So while we think we would already be treating by the time we get that low, your brain doesn't always function properly when your BG sarts to drop.

Jen  - LevemirConfused and Novalog Wink A1c 5.9 



Top 150 Contributor
Female
3 Posts
Reply
Sierra replied on Wed, Sep 23 2009 4:23 AM

Hi Ron,

 Thank you for a very good explanation. I understand that you are stating that  the plasma calibrated glucometer - glucose values is not much different from the lab values.

I am not diabetic but from a family with strong history of diabetes with my mum & bro currently on janumet, metformin, amaryl and novomix.

Is there any reference materials that I could refer to and show to my family?

Regards..Sue.

 

 

Top 150 Contributor
Female
3 Posts
Reply
Sierra replied on Wed, Sep 23 2009 4:26 AM

That's right and one should be very cautious when using any of the whole blood calibrated glucometers. Thank you for the info.. :)

Top 10 Contributor
Male
378 Posts
Reply
Ron AKA replied on Wed, Sep 23 2009 8:28 PM

The subject does not come up much as most now have the plasma calibrated meters. I use this Lifescan link to get my mind straight on it. You know, one is higher than the other, but the question is which way... Most meter companies will give their meters away, so it seems to me there is no need to deal with the confusion of using one calibrated to display whole blood values.

Ron

Not a med prof. Just diabetic type 2 on Prandin, Levemir, ramipril, indapamide, Crestor, & ASA. Diag. Feb/01.

"I have not failed. I have just found 10,000 ways that don't work." - Thomas Edison

Page 1 of 1 (7 items) | RSS
Joslin Diabetes Center and Joslin Clinic
One Joslin Place
Boston, MA 02215
© 2008 by Joslin Diabetes Center. All rights reserved. All materials contained on this site are protected by United States copyright law and may be used for personal, noncommercial use only. For permission for other use call (617-226-5815). You may not alter or remove any trademark, copyright or other notice from copies of the content.