Intense DAB Background can make the PDL1 interpretation difficult. Severe background should not be interpreted. Manufacturer has recommended to maintain high level of humidity within the instrument. We have achieved optimal results in the EZIHC lab by sealing the instrument and by adding boiling water within the instrument (see results below)

Manufacturer provides Positive and Negative Batch Control as Cell Pellet with know positive and negative PDL1 expression. A positive control is acceptable for the PD-L1 positive cell pellet if at least 70% of the cells contain cell membrane staining of at least 2+ average staining intensity. For the PD-L1 negative cell pellet, the following staining is acceptable the majority of cells should demonstrate no staining. The figure below shows an unacceptable negative bath control which has to be troubleshot directly with the manufacturer. Indeed these proprietary kits are sold with their own reagents and we cannot modify any parameter.