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Hi

I composed this reply on Wednesday:

I agree with Rita and others that there are important metrological and service quality specification issues here - deciding what the measurand is and if it can actually be measured by current technology, assessing the effect on uncertainty of using algorithms which require other measurements and statistical manipulations, and deciding whether all this is good enough to answer the relevant clinical questions.  

An IFCC reference method does exist for ionised calcium
Clin Chem Lab Med. 2000 Dec;38(12):1301-14.  IFCC recommended reference method for the determination of the substance concentration of ionized calcium in undiluted serum, plasma or whole blood.  Burnett RW, Christiansen TF, Covington AK, Fogh-Andersen N, Külpmann WR, Lewenstam A, Maas AHJ, Müller-Plathe O, Sachs C, Andersen OS, VanKessel AL, Zijlstra WG; International Federation of Clinical Chemistry and Laboratory Medicine. IFCC Scientific Division, Working Group on Selective Electrodes
so it should be possible to measure what we really want to know in those patients where it is clinically necessary, without having to resort to derived analytes, or am I missing something here (this is clinical an area I am woefully ignorant of - sorry!)?

.....

However, I have just opened the latest Annals and there is a highly relevant article by Paul Glendenning on measuring ionised calcium, which he thinks is the way to go clinically.  So we seem to have an authoritative view.

Best wishes to all.

Jonathan





On Tue, Jun 18, 2013 at 11:02 PM, Rita Horvath <[log in to unmask]> wrote:
Anders, what we in fact do is that we offer adjCa 8using our in-house validated equation) to a restricted group of patients and in a restricted albumin conc range only. We have informed our dr-s about the estimated nature of the calculation (which is only a very rough guide at best) and the need for proper ionized Ca measurement if clinically deemed necessary. This is all commented on lab resports too as a constant reminder. I think in the world of imperfect solutions the best we can do is to inform them clearly and be transparent about the uncertainties associated with our reported results. Just letting them do with results what they think might be right is not appropriate laboratory service, in my view, and in fact can cause harm to some patients.

Having said this, I have just recently lectured GPs on inappropriate laboratory testing and when I highlighted to them the concept of measurement uncertainty, biol. var, etc, they became very keen on us reporting results with the uncertainty estimate so that they can take that into account when interpreting lab data. The only anecdote I remember about such an approach is that one Australian lab tried this at least a good decade ago but nearly went out of business as dr-s did not like to see plus/minus figures and felt the lab was not good enough to give them the 'right' result...so they had to stop this practice...I often ask why do we bother then having big spreadsheets of uncertainty calculations if we rarely use this for clinical information - just to plse the accrediting body??? Wonder how many labs report results with uncertainty estimates (!!!NB: estimates)?

So this simple question on Ca leads us to a lot of conceptual issues we still failed to solve as a profession, I am afraid.

Kind regards, Rita
________________________________
From: Clinical biochemistry discussion list [[log in to unmask]] On Behalf Of Anders Kallner [[log in to unmask]]
Sent: Tuesday, 18 June 2013 11:07 PM
To: [log in to unmask]
Subject: Population based algorithms

Dear Rita
A pertinent question may be if laboratories shall calculate, correctly, what we  know is wrong or leave it to the clinicians to wrongly calculate what is wrong anyway. It is not always that two negatives cancel.
Best regards,
Anders

Anders Kallner, MD, PhD
Assoc. Professor (R)
Karolinska Univ. Laboratories
Stockholm SWEDEN
+46 8 51774943
[log in to unmask]<mailto:[log in to unmask]>

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