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Audit and internal quality control in immunohistochemistry
1Quantitative Biomarkers Group, Cancer Research Centre, Queens University of Belfast and Institute of Pathology, Royal Group of Hospitals Trust, Belfast BT12 6BA, Northern Ireland, UK. p.maxwell@pub.ac.uk
Insights
This study introduces a scoring system for internal quality control in immunohistochemistry. The system helps assess staining quality and identify problematic antibodies like neurone specific enolase (NSE).
Area of Science:
- Surgical Pathology
- Immunohistochemistry Quality Control
- Diagnostic Cytology
Background:
- Internal quality control (IQC) procedures for immunohistochemistry (IHC) are not consistently described.
- Standardized methods are needed to evaluate the reliability of IHC staining in surgical pathology.
- Existing positive and negative controls require a systematic approach for effective interpretation.
Purpose of the Study:
- To describe a novel method for internal quality control in immunohistochemistry.
- To introduce a scoring system for objective assessment of IHC slide quality.
- To evaluate the performance of frequently used antibodies using the proposed scoring system.
Main Methods:
- A retrospective audit of IHC cases and positive tissue controls over three years (1996-1998).
- Evaluation of 10 frequently used antibodies, focusing on test cases and monthly positive controls.
- Development of a scoring system (0-8) assessing staining intensity, uniformity, specificity, background, and counterstaining.
Main Results:
- The scoring system effectively classified staining as optimal (7-8), borderline (5-6), or unacceptable (0-4).
- Most antibodies demonstrated optimal or borderline staining quality.
- Neurone specific enolase (NSE) showed frequent unacceptable or borderline staining due to low intensity, poor specificity, and high background.
Conclusions:
- The developed scoring system provides a reliable method for assessing immunohistochemically stained slides.
- Routine implementation of such a scoring system is crucial for everyday internal quality control in pathology labs.
- Identification and potential exclusion of antibodies with consistently poor staining (e.g., NSE) improve diagnostic accuracy.
Aims:
Although positive and negative controls are performed and checked in surgical pathology cases undergoing immunohistochemistry, internal quality control procedures for immunohistochemistry are not well described. This study, comprising a retrospective audit, aims to describe a method of internal quality control for immunohistochemistry. A scoring system that allows comparison between cases is described.
Methods:
Two positive tissue controls for each month over a three year period (1996-1998) of the 10 antibodies used most frequently were evaluated. All test cases undergoing immunohistochemistry in the months of April in this three year period were also studied. When the test case was completely negative for a given antibody, the corresponding positive tissue control from that day was examined. A marking system was devised whereby each immunohistochemical slide was assessed out of a possible score of 8 to take account of staining intensity, uniformity, specificity, background, and counterstaining. Using this scoring system, cases were classified as showing optimal (7-8), borderline (5-6), or unacceptable (0-4) staining.
Results:
Most positive tissue controls showed either optimal or borderline staining with the exception of neurone specific enolase (NSE), where most slides were unacceptable or borderline as a result of a combination of low intensity, poor specificity, and excessive background staining. All test cases showed either optimal or borderline staining with the exception of a single case stained for NSE, which was unacceptable.
Conclusions:
This retrospective audit shows that immunohistochemically stained slides can be assessed using this scoring system. With most antibodies, acceptable staining was achieved in most cases. However, there were problems with staining for NSE, which needs to be reviewed. Laboratories should use a system such as this to evaluate which antibodies regularly result in poor staining so that they can be excluded from panels. Routine evaluation of immunohistochemical staining should become part of everyday internal quality control procedures.
