We investigated this problem by adding known amounts of whole blood to
pooled old CSF samples which we were about to throw away, mixing,
centrifuging and measuring protein on the supernatant. We weren't concerned
about glucose because normal plasma and CSF values are reasonably similar.
The conclusion was that anything more than 1:500 of blood:CSF increased the
total protein by a worrying amount, but that 1:1000 or less was OK.
But of course this is only half the problem, and we could probably have
worked that out by calculation without needing to do the experiment. How do
you judge whether any given CSF is bloodstained over that limit? We don't
want to have to scan every CSF sample for a quantitative Hb value, and
anyway the ratio of plasma proteins to red blood cells (Hb) will vary
between patients. Using a photograph of the dilutions before centrifugation
was really difficult to judge, so in the end we decided that any deposit of
red cells after centrifugation more than 1 mm across, indicated excessive
blood contamination. But this is dependent on the tube dimensions and the
amount of CSF, so it's not easy to transfer the results across
laboratories.
Any other bright ideas?
John
John Whitfield
Clinical Biochemistry
Royal Prince Alfred Hospital
Sydney, Australia
Phone (+61) 2 9515 5246
Fax (+61) 2 9515 7931
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-----Original Message-----
From: Frank Alvaro [SMTP:[log in to unmask]]
Sent: Friday, 5 July 2002 20:15
To: [log in to unmask]
Subject: BLOODSTAINED CSF
How do labs handle bloodstained CSFs (specifically for protein and
glucose)? It's relatively easy to reject a heavily bloodstained sample, but
what about those samples that, after centrifugation, have a small but
definite RBC pellet? Is there some way to determine how much bloodstaining
is acceptable (ie protein and glucose have not been elevated by a
clinically significant amount)? And if not, how do labs decide what samples
to accept and reject?
Frank Alvaro
Senior Hospital Scientist
Clinical Chemistry
South Western Area Pathology Service
Sydney, Australia.
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