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"Best estimate of ionised calcium" is a misnomer, since measured ionised calcium (unadulterated by yet another algorithm on the blood gas analyser) has a numeric result around half the "adjusted" calcium (Please - NEVER "corrected") which we report due to the divalent nature of the calcium ion. We should perhaps also add a rider when calculating which draws attention to the non-adjustment of the calculation for pH due to its significant effect on the calcium:albumin binding. There are those who advocate the adjustment of magnesium, but the adjustments applied seem to me to be approaching the limits of analytical precision of the magnesium assay. See : CLIN.CHEM. 31/2,244-246(1985) 244 CLINICAL CHEMISTRY, Vol. 31, No. 2, 1985 Relationships between Magnesium and Protein Concentrations in Serum Martin H. Kroll and Ronald J. Ell with best wishes Richard Richard Mainwaring-Burton Consultant Biochemist South London Healthcare Trust Queen Elizabeth Hospital, Woolwich Princess Royal Hospital, Farnborough Queen Mary's Hospital, Sidcup 020-8836-5724 mob: 07831-739876 -----Original Message----- From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Jonathan Kay Sent: 18 June 2013 13:47 To: [log in to unmask] Subject: Should we harmonise Ca adjustment formulas first? We should report all calcium results as best estimate of ionised calcium. (Read that again; it doesn't say "calculated value of what the total calcium would be if the albumin were something different".) This is better than "adjusted calcium" in two main ways that affect clinicians who are looking after the affected patients: * It fits with the explanation of how calcium affects excitable cells * it gives values that are consistent with those from blood gas analysers, iStats and other likely future devices. (The Tofaletti paper explains inconsistencies and difficulties in adjusting calcium results to some albumin value that the patient doesn't have, but I don't read it as showing any clinical advantages in reporting total calcium. I also don't think it considers this proposal.) Jonathan On 18 Jun 2013, at 13:33, Rita Horvath wrote: > Thanks Mike and Anders and I share your sentiments fully. I am not a great fan of any population based formulas and their application to individual cases either - and particularly so in case of eGFR which is still far from being a perfect estimate. > > However, Ca is over-requested as part of the CMP (i.e. Ca-Mg-P) panel or other commonly used test sets and is often misinterpreted. The common preanalytical issues of haemoconcentration or haemodilution due to problematic phlebotomy etc are so often overlooked when interpreting marginally 'abnormal' total Ca results, that even an imperfect adjustment is better than overinvestigation of total Ca results when in fact they are not even abnormal. Furthermore, I know that dr-s use old formulas (and the net is full of them) w/o knowing even the methodological problems and limitations of such calculations. > > Providing ionized Ca measurement for all Ca requests is just practically impossible, not to mention the costs and the extra time associated with it. Whilst I fully agree with all recommendations that propose ionized Ca instead of total Ca and adjustment for albumin, I think our efforts should then first go into eliminating the vast number of unnecessarily requested Ca and P or CMP test sets. If we could achieve that (???) then maybe the test volume would be manageable for measuring only ionized Ca for all. Until then, we are left with imperfect solutions which still might serve our clinicians better than doing nothing... > > In the era of harmonization, could we at least find out what labs are reporting as adjusted Ca (because many do!), so that at least we can judge the size of the potential problem? Wouldn't EQA schemes be good for exploring that? > > Kind regards, Rita > > ________________________________________ > From: Clinical biochemistry discussion list [[log in to unmask]] On Behalf Of mpeake [[log in to unmask]] > Sent: Tuesday, 18 June 2013 3:50 PM > To: [log in to unmask] > Subject: Re: should we harmonise Ca adjustment formulas first? > > With reference to the point raised by Anders Kallner on adjusted calcium algorithms, Professor Tofaletti, an international expert on this subject, also argues against the use of calcium algorithms in the attached article. > > This paper, "Is ionized calcium always right and total calcium always wrong", provides an elegant summary of important issues on how laboratories can best help clinicians with their calcium results. > > Michael Peake > (retired) > Biochemistry Department > Flinders Medical Centre > Bedford Park > South Australia > Australia > (618) 8443 3332 > Email: [log in to unmask] > > > > -----Original Message----- > From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Anders Kallner > Sent: Tuesday, 18 June 2013 2:22 PM > To: [log in to unmask] > Subject: Re: should we harmonise Ca adjustment formulas first? > > Dear Rita, > Don't you think it is about time that the profession stopped using these population based algorithms for individual patients? > In addition to the innate uncertainty of measuring the ingoing quantities the uncertainty of the algorithm should be considered -as you rightly point out. Furthermore, it is theoretically impossible to go from an average (the algorithm can be viewed as a kind of average) to an individual. You face the same problem as with the eGFR! > Cheerio, > Anders Kallner > > -----Original Message----- > From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Rita Horvath > Sent: den 18 juni 2013 02:46 > To: [log in to unmask] > Subject: should we harmonise Ca adjustment formulas first? > > David, I do not know the answer to your question but instead I have another question - in fact I asked this from mail base members months ago but received no meaningful answers that I could have summed up. This relates to the adjusted Ca formula: is there any harmonisation achieved on which formula to use for both BCG and BCP albumin methods? In-house formulas (that we also use in my lab for BCP albumin) all suffer from the lack of proper validation and they are dependent on population Ca and albumin data (e.g. my lab mostly serves hospital population and a lot of kids and it is hard to validate our formula e.g. by comparing adjusted Ca to ionized Ca data as the latter test is usually done in critically ill or in those who need blood gas measurements for various acute reasons). So before Pathology Harmony suggests that we shall all use adjusted Ca should we not work on harmonising the Ca adjustment formulas for the various albumin methods? I am sure there is a lot of variation out there...I am also certain that clinicians, using labs which do not provide adjusted Ca results, simply use the old and simple adjustment formula of Ca+0.02(40-albumin) which is accessible from the web or which allows simple calculations by head. Surely this is not applicable to BCP albumin. > > So may I repeatedly ask mail base members of 1/ what Ca adjustment formula your lab is using? > 2/ for which albumin method? > 3/ and for which Ca method? > 4/ Are there any exclusion criteria when the use of the adjustment formula is limited, 5/ and if so what comments do you put on lab reports? > > Kind regards, Rita > Prof. Andrea Rita Horvath, MD, PhD, EurClinChem, FRCPath, FRCPA Past President of the European Federation of Clinical Chemistry and Laboratory Medicine Clinical Director, SEALS North, Department of Clinical Chemistry Level 4, Campus Centre, Prince of Wales Hospital Barker Street, Randwick, NSW 2031, Sydney, Australia > Tel: (+612)-9382 9078 > Fax: (+612)-9382 9099 > Mobile No: (+61)-404 027 843 > > -----Original Message----- > From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of David Wright > Sent: Tuesday, 18 June 2013 1:09 AM > To: [log in to unmask] > Subject: Calcium Creatinine Clearance Ratio, CCCR > > Calcium Creatinine Clearance Ratio is used in the diagnosis of FHH. Currently setting up parameters on the Host computer to make CCCR available. A question to ponder.... > > Formula (e.g. Hammersmith) appear to use Serum Calcium and not Adjusted Calcium (Pathology Harmonization) in CCCR calculations. > Does using Adj Ca make a significant difference? Does using Adj Ca introduce more error into the calculation (various formulae for Adj Ca) or reduce a potential error (low or elevated albumin levels). > > Thanks > > David Wright > Lead BMS. Antrim > > ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical community working in clinical biochemistry. > Please note, archived messages are public and can be viewed via the internet. 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