Regarding urine catecholamines:
I would like to follow up a comment by Jeffrey Barron about catecholamines
being expressed as a ratio to creatinine. I realise that Jeffrey only
mentioned this as a trigger for further investigation, but if it useful it
would be a great boon to our patients. However I have my doubts...
With a 24 hour (or other timed) collection we are measuring the amount of
adrenaline (or whatever) produced over the time period. For example a 1 cm
secreting lesion producing the same amount of secretory products would give
the same increase in a big or a small person. Creatinine correction does
two things, it reduces the within-person variation due to changes in
hydration, but also corrects for body muscle mass. Thus the same lesion in
a person with a small muscle mass would produce a higher response than the
same lesion in a larger person when corrected for creatinine.
I know of a case where a "lesion", subsequently shown to be normal adrenal
was recently removed from a very small person, largely in response to
grossley elevated cats:creat ratio (plus severe hypertension plus lump on
the adrenals). The timed levels were borderline elevated on one of three
occasions I think.
I would be very inetrested if anyone has evidence supporting the use of
spot samples for creatinine, or interpretration of catecholamine:creatinine
ratios in timed collections (leaving aside the use of creatinine to help
determine adequacy of collection.
Regards,
Graham
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital, Sydney
Victoria St, Darlinghurst, 2010
NSW, Australia
Ph: (02) 8382-2170 Fax (02) 8382-2489
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