Our lab has been doing the HPLC-based assay (ADA) for TB
for about 10 years. In a 2 year retrospective study by St
George's Hospital of our results it was found that the
assay was over 90% predictive of TB for peritoneal/ascitic
fluids (we have equal success with pericardial fluid,
limited experience with CSF, and don't recommend plasma).
This accuracy is higher than PCR (which is about 75%)
For most of the time our turnaround was approx 3-5 hours,
so clinicians using our service tended to begin
antibiotic therapy immediately on our result, and await the
culture. In at least one case we know of, we were told this
saved the patient's life. So the test seems to have some
intrinsic merit, in terms of speed and accuracy, but only
if acted upon by the clinician.
More recently, the safety of handling fluids that are not
actually 'known' to be TB positive, but TB suspected, we
have overhauled our handling of the fluids, and they are
all filtered first in category 3 conditions. The filtering,
with just a simple disposable 2um filter, effectively
renders the fluid sterile but does not affect the assay.
The downside of this step is that it has dragged out our
turnaround to approx 4-6 days. Readers will be aware there
has been some debate on this list about whether such fluids
should be handled as TB positive, and there seems to be no
national agreement.
We previously (on this list) offered to pass on our method
(and train) any regional hospitals wishing to set up the
ADA assay for TB (they would need HPLC for our method:
previously published methods use a colourimetric method
which in our hands has not been quite as accurate).
We had to delay on our offer when it was decided to review
the method completely in terms of health and safety, and
swap to filtering. We are now in a postion to again offer
to assist.
We also have a fax information sheet. Please phone our lab
and ask any staff member for the TB info sheet to be faxed
to you.
Regards
John Duley
(I am away for 3 weeks)
----------------------
Dr John A Duley
Purine Research Laboratory
Guy's Hospital
London SE1 9RT (GB)
------------------------------
I received a request this morning for ascitic fluid adenosine deaminase on
an asian lady with suspected tuberculous peritonitis. I cannot get into
assay finder this morning so....
Does anyone know the merits of this test and of anyone in the uk performing
the test?
regards
martin myers
preston and chorley hospitals
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