Re: [Histonet] False positive AFB
You are correct that house made formalin and other reagents can contain AFB
if the water is contaminated - that is one reason that we always used a
negative control from the current day's workload. This is a check on fixation and
processing as well as on the staining procedure. I would suggest that you
repeatedly centrifuge 50 ml aliquots of tap water, decanting and centrifuging
another 50 ml until you can see some sediment in the centrifuge tube. Take this to
microbiology and have them culture for AFB.
In researching this problem, we noted that AFB has also been reported in
paraffin (the old Tissue Mat wafers) and growing in a 40 gal. formalin tank. It
is a problem that is not taken into consideration often enough.
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