As part of our protocol for urinary catecholamine collection we have
always required that urine should not be collected within 24 hours of the
patient having contrast medium, radioactive gallium for bone scans or
other nuclear medicine procedures. I must admit I am not entirely sure of
the scientific reasons behind this. Does anyone have any information ?
It happened again just recently. We obtained quite normal results for
dopamine, homovanillic acid and other metabolites in urine from a child
with suspected neuroblastoma but realised the sample had been
collected after radioactive gallium had been administered. Recollected
several days later the urine showed sky-high dopamine and HVA
confirming neuroblastoma. There was a flurry of "I told you so's" or "isn't
this extraordinary" but I am sure in few years time it will all be forgotten
and new generations of oncologists and nuclear medicine specialists will
again be insisting on saving time by doing all investigations on the same
day.
I suspect that free radicals generated from radioisotopes may destroy
the catecholamines and metabolites (they are very good reducing agents
and free-radical trapping agents) but I don't have any data on this.
Contrast medium can produce a very thick slurry of white sediment in
some urines after refrigeration and possibly catecholamines may adsorb
to this material. Changes in renal clearance are another possible
explanation. Do other laboratories have experience with this ?
John Earl
Neurochemistry Laboratory
New Children's Hospital
Sydney, Australia
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