We use same range with all results carrying the rider :
“Adjusted to alb of 40 g/L (NB assumes normal pH)”
“Keep it simple”, I say
Any calculation of additional parameters, ratios, factors (fudge/fiddle) can be fraught with pitfalls, and may bear little relationship
to the physiological reality, as well as being subject to the sum or product of the inaccuracies of the methods, as well as those of the calculation.
Let the doctors doctor their patients and not our results.
By the time we have collected enough data on our specific analysers (colourimetric or ionic, with or without pH
correction woops adjustment) for a specific patient (because we must not group patients unscientifically) the patient will be either better or not, and the analysers will be due for replacement anyway so we will have to start again.
with best wishes
Richard
Consultant Biochemist
Queen Mary's Hospital
Sidcup,
020-8308-3084
Please note new e-mail address :
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From:
Clinical biochemistry discussion list [mailto:
Sent: 15 October 2009 19:59
To:
Subject: Re: Adjusted Calcium
Have you tried the procedure reported in Ann Clin Biochem 1996;33:55? Three laboratories used it to derive their own equations from their own total calcium
and albumin data. To quote: "Within each laboratory adjustment of total calcium values for albumin concentration using algorithms derived from their own regressions gave values which, after small number of outliers were excluded by probit analysis, were identical
with those in health".
I, too, had hoped to use normal ionized calcium values in patients with a wide range of albumin concentrations to construct a definitive equation. Unfortunately we found that measured ionized calcium is lower the lower the protein concentration due to a positive
interference of protein at the hypertonic reference electrode of commercial analyzers (references to 11 years (!) work in Clin Chem 1993;39:1082).
Don't give up yet!
Brian Payne
James J Miller wrote:
We are not calculating the albumin adjusted calcium. The clinicians do it themselves. However I have considered doing and reporting the albumin (and other analyte) adjusted calcium. Indeed, whether albumin alone or in combination with other calcium binders,
e.g., phosphate, I have been unable to come up with a reasonable formula that would adjust to the total calcium reference range. Use of ionized calcium in this effort was also not fruitful (so far). It would seem to me that a reference range (interval) for
the particular adjustment (and analyzer) would be the way to go. I guess patients with a normal ionized calcium could be used to derive that reference interval.
-Jim
>>> "Collins Wayne (LTHTR)" <[log in to unmask]> 10/15/2009 12:08 PM >>>
Dear all
I am interested to know what others use as a “
Wayne Collins
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