Brian Payne did a lot work on this subject.
If I remember right his conclusions were:
1. BCP gave results closer to immunoassay results.
2. corrected calcium results were closer to ionized calcium when BCG
method was used especially when the albumin is low. this is
probably due to the fact calcium binds to other proteins as well and
this binding increases at low albumin concentration. BCG method
'measures' these 'other' proteins at low albumin values. Thus the
corrected calcium calculated using BCG albumin is better correlated
with ionised calcium.
Swami
On 5 Oct 00, at 13:37, Eric Kilpatrick wrote:
We ran into the problem of corrected (I prefer the word 'adjusted') calcium
when we changed from BCG to BCP albumin after we moved over to Beckman LX20
analysers. The BCP was lower at the lower end and higher at the higher end
than BCG which made usual adjustments e.g total calcium + 0.02(40 -
albumin), inappropriate.
The answer we used was to employ Julian Barth's method (Ann Clin Biochem
1996; 33: 55-58) which uses lots of your own lab patient data to plot total
calcium vs.albumin over the albumin range 20-55g/L, excluding patients with
abnormal urea/creatinine/AST/alk phos/potassium. You end up with a pretty
linear graph whose regression line is your adjustment formula. In fact, we
calculated the regression equation indices so that the 95% confidence limits
i.e. the ref interval, were whatever we chose them to be (in our case 2.20 -
2.60 mmol/L). As a result, the adjustment means this is one of the locally-
derived reference intervals that I have most confidence in.
As an aside, we still did not know whether it was BCP or BCG which was
giving us the 'right' answer, but interestingly an immunoassay for albumin
gave values to within 1g/L of the BCP method and miles from the BCG one.
Dr. Eric S. Kilpatrick
Consultant in Chemical Pathology
Hull Royal Infirmary
Anlaby Rd
Hull HU3 2JZ
Tel: 01482-607708/607743
THIS DOCUMENT HAS NOT BEEN SPELLCHECKED
----- Original Message -----
From: JOE BEGLEY <[log in to unmask]>
To: acb mailbase <[log in to unmask]>
Sent: Thursday, October 05, 2000 10:22 AM
Subject: Corrected Calcium
> Some views on current practice would be appreciated. Do members:
> 1) Automatically issue a corrected calcium on all requests
> 2) What formulas are used?
> 3) Is correction valid at all albumin levels or just low levels.
> Thanks
>
> Joe Begley
> Poole Hospital
>
>
Prof.R.Swaminathan
Department of Chemical pathology
St.Thomas' Hospital
London SE1 7EH
Tel 0171 955 4010
Fax 0171 928 4226
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