What are Controls in Histology?
In
histology, controls are critical tools used to verify the accuracy and reliability of staining and other diagnostic procedures. They help ensure that the results obtained from tissue samples are valid and can be confidently interpreted. Controls serve as a benchmark to compare the experimental samples, indicating whether the staining or detection methods have worked as expected.
Validation: Controls confirm that the staining methods and reagents are functioning properly.
Comparison: They provide a standard to which experimental results can be compared.
Reproducibility: Ensuring consistency across different experiments and laboratories.
Quality Control: Identifying technical issues or errors in the preparation and staining process.
Types of Controls
There are several types of controls used in histology, each serving a unique purpose:Positive Controls
Positive controls are tissues that are known to react positively to the stain or antibody being used. They confirm that the staining protocol works and that the reagents are effective. For instance, if you are staining for a specific protein, a tissue sample known to express that protein would serve as a positive control.
Negative Controls
Negative controls are tissues that should not react to the stain or antibody. They help identify any non-specific binding or background staining. For example, a tissue sample that does not express the protein of interest would be used as a negative control.
Internal Controls
Internal controls are elements within the same tissue section that provide a built-in comparison. These are particularly useful in immunohistochemistry and
in situ hybridization, where certain cell types within the tissue may serve as natural positive or negative controls.
External Controls
External controls are separate tissue samples processed alongside the experimental samples. They are treated in the same way as the experimental tissue to ensure consistency across different slides and experiments.
Consistency: Controls should be as similar as possible to the experimental samples in terms of tissue type, fixation, and processing.
Specificity: Positive controls should express the target antigen or marker, while negative controls should not.
Availability: Controls must be readily available and reproducible to ensure consistent results across different experiments and laboratories.
Common Issues and Troubleshooting
Even with the use of controls, issues can arise:Non-Specific Staining
Non-specific staining can be identified using negative controls. If non-specific staining is observed, it may indicate issues with
antibody specificity or the need for optimization of the staining protocol.
Weak or No Staining
Weak or absent staining in positive controls suggests potential problems with the reagents or staining protocol. This may require adjustments in antibody concentration, incubation times, or detection methods.
Batch-to-Batch Variability
Using external controls processed alongside experimental samples helps identify batch-to-batch variability. Consistent results across different batches confirm the reliability of the staining methods.
Conclusion
Controls are indispensable in histology, providing the necessary benchmarks to validate and interpret experimental results. By carefully selecting and applying positive, negative, internal, and external controls, histologists can ensure the accuracy, reliability, and reproducibility of their staining and diagnostic procedures. Proper use of controls ultimately enhances the confidence in the histological findings, contributing to better
diagnostic accuracy and research outcomes.
