I have a conundrum...
A 50-ish year old lady presented 4.5 hours following paracetamol
overdose of unknown quantity (taken at 8.30 am). No other
significant drugs taken (I can't recall exactly what else she
took - but the triage nurse phoned guys and was advised that the
most significant problem was with the paracetamol and that the
other drugs, whatever they were, wouldn't affect the paracetamol
levels).
Four and a half hour paracetamol level of 127. Lab error
discovered at 8.30 pm - they phoned through having re-run the
test on the same sample... paracetamol level of 254. At the
time that I re-sited the iv to start the NAC I took another
specimen - just over twelve hours after the overdose - and sent
it to the lab. I figured that with two levels on one specimen
that were clinically significantly different it would be wise to
check it again. The twelve hour level came back as 270. So,
the level went UP from four and half hours to twelve hours post
ingestion.
Both the re-test of the first sample and the test of the second
sample were done with the same batch of reagent.
The patient is not on any enzyme-inducers and is not a heavy
drinker.
I phoned the consultant biochemist who told me that he had seen
this before, he didn't regard it as extremely unusual for the
paracetamol level to continue to rise after four hours.
So. I understand that a graph is just a graph and that their
will always be extraordinary exceptions - but the results above
and the words of the biochemist give me cause for concern over
the use of the paracetamol overdose nomogram.
Can anyone suggest what might have happened? Has anyone else
experienced the same problem?
Sarah Spencer
SpR, Oxford Region
PS Complicated reasons for patient still being in department 12
hours post ingestion - but it's just as well she was!
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