I would tend to agree that the immuno control issue is all about finding the balance between technical adequacy, pathologist confidence, economics and logistics. We are constantly trying to achieve this balance, by fine-tuning our control requirements accordingly.
Often, we'll receive a request for marker(s) for more than one block of a case. We do not pick up a section from each block on a control. One control for the case (usually on a slide with one of the patient sections) is adequate for us. Taking that one step further, if two or three cases are on a run (Ventana BenchMark XT), for the same marker(s), we require only one control per marker per run. The one control per marker per pathologist idea was done away with long ago, they can share controls!
Control and patient section on the same slide halves reagent costs, number of slides to coverslip and store, and allows more cases to tested per run. One exception being if unstained slides were cut on a small biopsy, we have to stain these and the control slide separately, as the tissue of interest may not be in the block after a deeper level was cut for routine staining.
If we have any suspicion that an instrument or dispenser error has led to a false negative, that test is repeated. As Sate said, the internal positive controls and staining patterns are well-known to IHC techs and pathologists. We assess our positive controls before sending cases to the pathologists, although this may not be done in all centres,in which case the pathologist alone performs this function.
Have a great weekend,
Eric Gagnon MLT
Kingston General Hospital
Kingston, Ontario, Canada
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