In labs that I ran in the past, we omitted the primary antibody and
substituted with primary antibody diluent.  At one time, we put affinity
purified mouse IgG and rabbit IgG (10 micrograms per ml in primary
antibodies diluent).  However, for the CAP inspection, it didn't seem to
make any difference what we did, as long as I ran a positive control and
negative control with each test.  If I had 10 different antibodies on
one patient, one block, I would run 10 different positive controls and
one negative control.  For my negative control I substituted PBS for the
primary antibody.  This was satisfactory for the CAP inspection.

In reality, a true negative control is difficult to produce.  You would
have to take primary antibody you are using, such as L26, and absorb out
the B-cell specific antibody.  Then you would dilute it with an antibody
diluent, and dilute it at the same concentration as your working titer
for L26 .  Obviously, that is not going to happen.

So, I guess what it comes down to is what does CAP require for a
negative control?  I think it would be fun to do a survey.  Let's see
what we all use.

A.  PBS
B.  Antibody Diluent
C.  Non immune control serum.  What kind and what concentration?
D.  All of the above.

What does CAP require?


David Tacha