Dear All

I must confess to having been rather, well, negative about negative
controls in my time but I think that the recent discussion has been very
useful. Here is my two pence worth...

CAP: I expect that what any accrediting body *really* wants to see is a
policy, backed up by operating procedures that interpret the policy and
evidence that these procedures are being followed. To this end I thought
that Marjorie's contribution was clear and concise. Also it made sense
technically, more of which anon.

Controls: It would seem there are three types of negative control-
1. Omission. Here the primary Ab is omitted and a solution applied which
is either Ab diluent or rinse buffer. All these tell you is that your
secondary Ab does not cross react with human tissue. You might be
justified in running such a control when you start a new batch of
secondary but to run it on every case is pointless.
2. Substitution. Here a non-immune serum from the same species as your
primary is applied in diluent. This is probably justified but raises
other problems. See below.
3. Absorption. Here the primary Ab is reacted with its own antigen and
the resulting mixture applied. Can't be done, as David Tacha quite
rightly pointed out. Which is a shame because this would be a *true*
negative control.

Substitution with non-immune serum would seem to be the best approach
but how do you know a) which class of immunoglobulin to use and b) which
dilution to run it at. Well if I were a huge international IHC company
with a name beginning with D, I think I would try to advise my customers
on the right policy and give them the products to back it up.

Would it be too difficult for such a company to market a range of non-
immune control sera, clearly labelled and colour-coded, and cross
reference this to their primary range such that if we use their L26, the
data sheet recommends control serum #xxx run at 1:xx?

--
Jim Elsam
HTEQA Services