Positive quality control slides ensured all techniques were appropriately executed, resulting in successful staining. They verified that antigen retrieval was utilized correctly, all reagents were mixed and applied properly, antibody dilutions and the method of staining were correct, and the incubation times and temperatures were optimal. Tests on patient tissue should not be considered valid if positive control tissues fail during staining and results are negative.
A positive tissue control must also be stained each time an IHC stain is performed on patient material. Known positive tissue may be found in the performing laboratory, or commercially purchased slides may be used. However, the tissue found in the performing laboratory is optimal to ensure control tissues undergo the same fixation, processing, and sectioning conditions as the patient tissue.
The primary antibody product insert sheet lists the best positive tissue for quality control. A positive control section is a must with every antibody that is used. Ideally, the positive control section should be mounted on the same slide as the patient tissue section to ensure that all tissues are treated equally. A positive control tissue on each slide can help identify uneven staining if you use an automated stainer that may not be adequately leveled. It will also help identify inconsistencies in mixing the reagents that appear to have spotty staining on the control tissue. Patient slide staining should be considered invalid when positive controls do not perform as anticipated. Neither control nor patient slide should be provided to the Pathologist. Repeat staining is required.
