Over the last few years we have been asked occasionally to measure fecal
electrolytes and sometimes also osmolality. This can be either to aid in
distinguishing between osmotic and sectretory diarrhoea or to monitor
electrolye loss in severe diarrhoea. In many cases the sample is solid and
usually this is because the test was not thought of, or the sample not
collected, until the diarrhoea has abated. In nearly all cases a call to
the doctor has confirmed that these measurements are not required on solid
samples.
For fluid samples, thorough mixing followed by centrifugation, possibly
with added filtration seems to be sufficient to provide a useful sample.
With loose or semi-solid samples mixing 1:1 with distilled water seems to
be sufficient.
Additionally see Tietz Textbook for interpretation.
I would be intrested in any other comments on this issue.
Yours,
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
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