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Bicarbonate didn't use to be a problem, until the twin evils of top sampling and high volume systems came along.
Kent C. Dooley PhD FCACB
Clinical Chemist
LifeLabs
3201 - 4464 Markham Rd.
Victoria BC V8Z 7X8
tel: 250 881-3100 ext. 2120
email: [log in to unmask]
web: www.LifeLabs.com
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Jonathan Kay
Sent: Tuesday, February 22, 2011 10:14 AM
To: [log in to unmask]
Subject: Bicarbonate assay
Why do we measure bicarbonate in uncapped specimens in a central laboratory rather than on blood gas analysers?
Jonathan
On 22 Feb 2011, at 17:45, Dooley, Kent wrote:2nd paragraph (below) should read "simply" not "sampling".Automatic spelling correctors(sigh)Kent C. Dooley PhD FCACBClinical ChemistLifeLabs3201 - 4464 Markham Rd.Victoria BC V8Z 7X8tel: 250 881-3100 ext. 2120email: [log in to unmask]web: www.LifeLabs.com-----Original Message-----From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Dooley, KentSent: Tuesday, February 22, 2011 9:36 AMTo: [log in to unmask]Subject: Re: Bicarbonate assayI suspect that much of the confusion around Bicarbonate standardization (we have had similar problems with Siemens bicarbonate)arises from modern chemistry analysers sampling from the top few millimetres of the specimen. Since CO2 can diffuse rapidly into the air but (H2CO3) diffuses more slowly in aqueous solution, one would expect there to be a layer of depleted bicarbonate at the air-liquid interface.We have conducted a small experiment on our Advia 1800 where we let specimens sit undisturbed on the analyser and have seen significant(sic) decreases in bicarbonate in 30 minutes. The changes can be "eliminated" by sampling mixing the tube.In many large volume labs samples can sit on a track for considerably longer than 30 minutes.I suspect that this phenomenon and manufacturers attempts to meet the demands of their largest customers confers confusion on the process of assigning calibrator values.Kent C. Dooley PhD FCACBClinical ChemistLifeLabs3201 - 4464 Markham Rd.Victoria BC V8Z 7X8tel: 250 881-3100 ext. 2120email: [log in to unmask]web: www.LifeLabs.com