Ionized calcium is not entirely reliable in patients with
hypoalbuminaemia - in patients from two hospitals with no obvious
disturbance of calcium homeostasis or acid-base balance we found that a
mean difference of 10 g/L in BCG albumin was associated with a mean
difference of about 0.05 mmol/L in ionized calcium measured on
Radiometer and Nova machines (Correlation between serum ionised calcium
and serum albumin concentration in two hospital populations. BMJ 1984;
289: 948-50).
So the true ionized calcium in Dermot's patient with a measured value of
1.26 mmol/L and an albumin of 26 g/L - if it was measured with BCG and
not BCP - might be more than 1.31 mmol/L , above the usual reference
range of about 1.14 - 1.28 mmol/L.
Brian Payne
Dermot Neely wrote:
>Here are anonymised data from an actual case from 2 years ago which
>illustrates that this problem does exist (at least in parts of the North
>East!)
>
>Patient AGE 54 DOB 03/03/44 SEX F
>Clinical Details: Myeloma IgAK paraprotein Approx 50g/L. No apparent bone
>or renal disease but hypercalcaemia as repeatedly measured on standard
>Roche/Hitachi system (results in reverse date order):
> 1 04/11 1302
> BONE CA 3.19 C PHOS 1.14 ALP 46 C ALB 26 L CA ADJ 3.47 C
> 2 04/11 1302ICA
> ICA (Ionised Calcium) 1.26
> 3 04/11 1100
> BONE CA 3.11 C PHOS 1.11 ALP 48 C ALB 25 R CA ADJ 3.41 C
> 4 27/10 1057
> BONE CA 3.15 C PHOS 1.24 ALP 48 C ALB 26 L CA ADJ 3.43 C
> 5 21/10 1406
> BONE CA 2.96 H PHOS 0.96 ALP 51 L ALB 27 L CA ADJ 3.22 C
> 6 21/10 1406
> UE NA 138 K 3.5 UREA 5.1 CREAT 90 CL 105 CO2 24
>AGAP 13
>
>Haematologist correctly withheld bisphosphonate on clinical grounds as
>patient was asymptomatic, a decision supported by the normal ionised
>calcium. Treatment is therefore best based on ionised calcium results and
>clinical assessment in this situation.
>
>Dermot
>
>-----Original Message-----
>From: Horsman Graham
>[mailto:[log in to unmask]]
>Sent: Thursday, 21 November, 2002 2:40 PM
>To: [log in to unmask]
>Subject: Monoclonal proteins and calcium binding
>
>
>Whilst on the thread of data interpretation and its relationship to one's
>own clinical practice, one of the SHOs here brought the following question
>fresh from the recent MRCP and to the best of his memory it goes as follows:
>
>60 year old man with known multiple myeloma. Corrected calcium 3.3 mmol/l.
>Treatment included both palmidronate infusion and clodronate and corrected
>calcium was 3.13 mmol/l a few days later.
>
>Other data included Total protein 88 g/l
> Albumin 25 g/l
> Ionised calcium: exact value forgotten but low / low
>normal
>
>The choice of five responses realistically narrowed down to the patient
>being resistant to bisphosphonates, and the result of the calcium binding by
>the monoclonal protein, which I expect got the marks.
>
>The question is does anybody have experience of how common a phenomenon is
>hypercalcaemia due solely to monoclonal globulin binding? My prejudice has
>been that it is a phenomenon described in the books but not commonly seen in
>practice, but I haven't routinely looked for it so a prejudice it remains.
>It is not acknowledged in the recent (2001) myeloma guidelines from the
>British Committee for Standards in Haematology
>
>As it has featured in MRCP there may be a short run of requests on it.
>
>I would be grateful for the views / experience of others about this.
>
>Dr Graham Horsman MSc MB MRCP(UK) MRCPath DCH
>Consultant Chemical Pathologist
>Department of Clinical Chemistry
>Burnley General Hospital
>Casterton Avenue
>BURNLEY BB10 2PQ
>
>Tel 01282 474297
>Fax 01282 474289
>
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