Which methodology do you use to measure calcium. One of the methodology
problems is the pH in the Arsenazo dye method, where acid pH
precipitates the raised proteins and falsely raise the analysed
Calcium. This can be verified if you reanalyse the sample using 
o-cresolphthalein method as described in the annals. 

Hope this is useful.
With kind regards
Vivek
Guy's & St.Thomas' Hospitals

On Mon, 17 Apr 2000, [iso-8859-1] Mohammad Al-Jubouri wrote:

> Dear all
> 
> I wish to share this interesting case with you. Last
> week, a high serum calcium of 4.11 mmol/L was brought
> to me to deal with. The result belongs to a
> 66-year-old gentleman who was admitted to a surgical
> ward because of right upper quadrant pain. The
> surgical Spr told me that the patient is fully
> conscious, orientated, has no polyuria or polydipsia
> with no clinical evidence of malignancy and is feeling
> well in himself. Despite this, I told him that he
> should be managed as a hypercalcaemic crisis which is
> probably due to underlying malignancy. Meanwhile, a
> serum protein electrophoresis was performed which
> showed an intense paraprotein band (57 g/L)which
> immunofixed as IgG lambda. A random urine sample
> showed heavy Bence-Jones proteinuria (3.5 g/L). The
> patient received 90 mg pamidronate infusion and his
> repeat calcium 24 hours late was 4.23 mmol/L!! To
> investigate the possibility of spurious hypercalcamia,
> the immunoglobulins were precipitated from the sample
> by PEG and calcium was re-measured in the supernatant
> which gave a result of 2.34 mmol/L. It became obvious
> that this hypercalcaemia was spurious due to binding
> of the calcium to the paraprotein molecules. The other
> clues which point to this phenomenon are the absence
> of clinical features of severe hypercalcaemia and
> failure of response to pamidronate infusion. Ionised
> calcium measurement would have picked up this
> instataneously, but we do not have this assay. So far,
> I have seen at least 3 such cases associated with
> paraproteinaemia, yet this phenomenon is not widely
> described in the literature. Comments regarding
> similar experience are welcome.
> 
> Regards.
> 
> =====
> Dr. M A Al-Jubouri
> Consultant Chemical Pathologist
> Whiston Hospital
> Prescot
> Merseyside L35 5DR
> UK
> 
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