[Histonet] RE: negative IHC controls

[Bryan Hewlett]

Dear Hadi,

I agree with much of the content of your posting. However, there seems to be
a mixed message here.
You agree that; (a) running multiple reagent control sections covering the
appropriate antibodies/pretreatments is ideal and that, (b)  money should be
well spent on QC (which you emphasize), yet you seem to downplay the use of
complete reagent controls and to inject some confusion regarding the
necessary use of process controls.

Process controls are intended to address the full range of procedural
variables and to ensure that the end result of the process is known to lie
within legitimate or acceptable values and is valid. Process controls are a
necessary tool utilized PRIOR to the subsequent interpretation of the
result.
Subsequent interpretation of the result depends largely upon the validity
provided by these process controls. No one has suggested that a reagent
control on the patient slide is the only way to recognize a false positive
signal. In fact, the experienced observer provides the final additional
level of process control.
However, that does not mean that all the necessary prior process controls
can be avoided or omitted by that experienced observer.
We too, have seen 100's of IHC stains daily and the full use of process
controls has been an important factor in obtaining consistent results.
We have seen numerous occasions where reagent controls have provided
essential clues to the nature of an aberrant finding.
I would have to disagree with you that a single reagent control is more than
sufficient.

I do agree with your comments regarding the use of one positive 'external'
tissue control per antibody/ per run but would point out that, if the
positive 'external' control works and the patient 'expected' positive
internal controls didn't, repeating the antibody test, using the same
process, should produce exactly the same result!
That would mean that either the 'expected' result is not a valid
expectation, or that the process controls are inadequate and do not account
for all of the procedural variables.

Regards,

Bryan Hewlett


On Friday, October 10, 2003, at 10.06 PM, Hadi Yaziji wrote:

Theoretically, I agree with you that (a) running multiple negative control
sections to cover the different antibodies/pretreatments is ideal and (b)
money         should be well spent on QC (I can't emphasize that enough).
However, I honestly don't remember when was the last time when I had a false
positive             staining on a patient's slide that the negative control
was the only way that allowed me to recognize the false positive signal on
the real slide. And we         look at 100s of IHC stains every day.
........

Experienced pathologists and technologists can still recognize in > 99% of
the times a false positive signal from a real signal on the tissue section
of a given antibody without even having to look at negative controls. ...

Individuals who perform and interpret IHC studies must have the knowledge to
recognize the expected sub-cellular localization of every antibody on every
type of tissue, including aberrant signals....

All you need is one positive control per antibody, but not one control/per
antibody/per patient. In many cases positive internal controls are present
on the same slide, so you can tell whether your antibody worked simply by
evaluating the expected positive internal controls. In fact, if your
positive 'external' control worked and internal controls didn't, then you
need to repeat your antibody test regardless of the positive external
control........

The bottom line: in real life, one negative control per case is more than
sufficient. And to say the least, it's inaccurate to state this is poor
patient care and lousy quality control.