How are semi-quantitative IHC tests interpreted?

How are semi-quantitative IHC tests interpreted?

• A. By measuring exact concentration of antigen
• B. Based on arbitrary scoring range (0 to 3+) that reflects antigen expression by means of the staining intensity and distribution as well as percentage of positive cells, calibrated against reference controls
• C. By counting total cells
• D. By comparing to a completely different assay

Answer: (B)

The idea behind interpreting semi-quantitative IHC is to translate what you see under the microscope into a practical score that reflects how much antigen is expressed and how widespread it is in the tissue. In practice, pathologists assess staining intensity in the positively stained cells (none, weak, moderate, strong) and estimate the proportion of cells that show staining. These observations are then combined into an arbitrary scoring range, commonly 0 to 3+, with higher scores indicating stronger expression and/or greater distribution. Crucially, this scoring is calibrated against reference controls run with the batch, so the interpretation is consistent and comparable across runs and laboratories. This approach provides a semi-quantitative, relative measure of expression rather than an exact concentration, acknowledging the variability inherent in IHC. It’s not about counting all cells to get a number, and it’s not based on comparing to a completely different assay.

The idea behind interpreting semi-quantitative IHC is to translate what you see under the microscope into a practical score that reflects how much antigen is expressed and how widespread it is in the tissue. In practice, pathologists assess staining intensity in the positively stained cells (none, weak, moderate, strong) and estimate the proportion of cells that show staining. These observations are then combined into an arbitrary scoring range, commonly 0 to 3+, with higher scores indicating stronger expression and/or greater distribution. Crucially, this scoring is calibrated against reference controls run with the batch, so the interpretation is consistent and comparable across runs and laboratories. This approach provides a semi-quantitative, relative measure of expression rather than an exact concentration, acknowledging the variability inherent in IHC. It’s not about counting all cells to get a number, and it’s not based on comparing to a completely different assay.