I fear that potassium is the hardest analyte of all on which to give
opinions.
Visible or measured "Haemolysis" refers to the escape of haemoglobin from
the cells due to membrane disruption. This will also release potassium into
the serum, but unlike haemoglobin, the homeostatic mechanism for potassium
(and sodium) will continue to function in vitro as long as there is a supply
of glucose and ATP. Thus the potassium abnormality may well be redressed
(totally or partially) by the time the sample is presented to the analyser.
Thus to give a quantitative estimate of what the potassium might be is not
wise. Nevertheless, should the potassium be low, a comment indicating the
possibility of its being even lower should be made.
The corollary to this is the 'old' sample in which the glucose supply has
been exhausted resulting in potassium leak due to cessation of the
sodium:potassium homeostatic mechanism, but not haemoglobin release since
the membrane is still structurally intact. Thus the sample is not
"haemolysed" but the potassium is rubbish. If we are going to be totally
scientific and consistent, we should measure the glucose on the serum/plasma
sample and compare that with the fluoride sample and make an estimate of....
let's not go there !
This also indicates that the manufacturer-quoted effects on potassium due to
"haemolysis" induced by the addition of different amounts of haemoglobin
bear little or no relationship to the true physiological situation.
with best wishes
Richard
Richard Mainwaring-Burton
Consultant Biochemist
Queen Mary's Hospital
Sidcup, Kent
020-8308-3084
-----Original Message-----
From: Graham Jones [mailto:[log in to unmask]]
Sent: 22 October 2007 23:25
To: [log in to unmask]
Subject: Re: haemolysis indices
Dear Colleagues,
Regarding reporting results with known interferences, I think that there
is a middle road between withholding and giving out with a comment (eg
"interpret with caution"). The problem with the former is that important
information may be with-held, and with the second that the vast majority
of clinicians have no basis for making sense of the possible effect. Not
only have they never seen haemolysis (they collect and send whole blood)
but they have no basis for determining the possible magnitude of an
effect even if they know its quality (eg K goes up with haemolysis). I
suggest that for many interferences for many analytes the nature and
extent of the interference is known, within limits.
A useful response to a measured potassium 5.4 mol/L with moderate
haemolysis measured by serum indices may be to replace the result with a
link to a footnote as follows:
POTASSIUM: Sample moderately haemolysed (free haemoglobin 200 mg/dL).
This may increase measured potassium. Provided intravascular haemolysis
can be excluded true potassium is likely to lie between 4.4 and 4.8
mmol/L.
The clinician can then decide whether this range of results answers the
question. Of course it does not exclude other effects on potassium.
Regards,
Graham
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Ph: (02) 8382-9160
Fax: (02) 8382-2489
>>> "Mainwaring-Burton Richard (RGZ)"
<[log in to unmask]> 10/18/07 6:33 PM >>>
Dear All
We are currently using haemolysis indices on Abbott Architect analysers
in
an attempt to apply some science to the previous rather subjective
eyeballing technique.
On the basis of the 'level' of haemolysis, we obliterate and comment
results
for groups of tests identified as sensitive in the manufacturer's
information. The process is carried out on the LIMS so raw results are
still
available on the analyser.
This has caused particular upset amongst the paediatricians who all but
demand the right would like to see the result so that they can make
their
own decision regarding its relevance. I should add that if the result
is
contrary to the expected interference (eg low potassium, magnesium or
phosphate in the light of haemolysis) the result is reported and extra
attention is drawn to the result.
My view is that we should not report results which are known to have an
error-factor, in the same way that results from a drip arm should all be
ignored.
Any other views ?
with best wishes
Richard
Richard Mainwaring-Burton
Consultant Biochemist
Queen Mary's Hospital
Sidcup, Kent
020-8308-3084
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