Sample Collection and Handling
Proper sample collection and handling are the first steps in maintaining histology standards. Tissue samples must be collected in a manner that prevents degradation or contamination. This involves using appropriate collection tools, timely fixation, and correct labeling of samples to avoid mix-ups.
Fixation
Fixation is a critical step that preserves tissue morphology and prevents autolysis. The most commonly used fixative is formalin, but other fixatives like glutaraldehyde or Bouin's solution may also be used depending on the tissue type and the analysis required. The fixation time and concentration must be standardized to ensure consistent results.
Processing
Tissue processing involves dehydration, clearing, and infiltration with a medium like paraffin that supports the tissue during sectioning. Each step must be meticulously timed and monitored to ensure that the tissue is adequately prepared, minimizing artifacts that could affect the outcome.
Sectioning
Once processed, the tissue is embedded in paraffin and sectioned using a microtome. The thickness of the sections is standardized, usually between 3-5 micrometers, to ensure uniformity. The microtome must be well-maintained and calibrated regularly.
Staining
Staining enhances the contrast of tissue structures, making them visible under a microscope. The most common stain is Hematoxylin and Eosin (H&E), but other specialized stains like PAS, Masson's Trichrome, or immunohistochemical stains may be used. Standardized staining protocols ensure that the results are reproducible and comparable across different laboratories.
Quality Control
Quality control (QC) measures are essential to verify the accuracy of histological processes. This includes regular calibration of equipment, use of control tissues, and periodic proficiency testing. QC helps in identifying and correcting deviations from established standards.
Documentation and Record Keeping
Accurate documentation and record-keeping are crucial for traceability and accountability. This includes maintaining detailed records of all samples, the methods used, and the results obtained. Proper documentation ensures that any issues can be traced back and rectified, and it provides a valuable resource for future reference.
