I write regarding Mike Addisons case of the surprising high pCO2 in the
polycythaemic girl.
Unfortunately I have no explanation but a recent somewhat similar
experience. In performing an ionised calcium on a freshly collected venous
serum sample from a 53 yo woman we found a pCO2 of 69.2 mmHg an O2 of 27.1,
a pH of 7.22 and a bicarbonate of 27.1 mmol/L. Additionally the ionised
calcium was 1.39 mmol/L (1.1 - 1.3 mmol/L) which the instrument corrected
to a normal value of 1.26 mmol/L.
We remeasured the sample (serum) and a simultaneously collected heparin
plasma sample on a different blood gas machine and got similar answers.
All the measurements were made on Radiometer ABL 620 analysers.
The patient was a chronic smoker but had no obvious respiratory symptoms.
We have seen this type of picture (only much more severe) with serum
samples transported in dry ice but we could find no exposure of the sample
in this case.
We repeated the collection (quick, clean venous collection transported
immediately to the lab) and got very similar answers.
In discussion with the physician, as I was unable to provide any
artefactual causes, I suggested referral to a respiratory physician and a
formal arterial blood gas. We noted the lack of metabolic compensation but
this did not help our cause.
I am told that she has had an arterial blood gas, presumeably elsewhere,
with a normal result!
She was not polycythaemic.
I am interested in the type of blood gas machine that you have at
Manchester, Mike.
Yours very puzzled,
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
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