Pathology is the study of disease through the examination of tissue and cells. The pathology workflow is the organized sequence of steps a tissue sample follows from the moment it is removed from a patient until a final diagnosis is issued. This sequential process ensures the integrity of the results, as the successful completion of each stage is necessary for accurate diagnosis. Every step is monitored carefully to ensure the tissue appearance accurately reflects the patient’s condition, guiding treatment planning.
The Initial Steps of Specimen Handling
The first stage, known as the pre-analytical phase, focuses on securing and preserving the physical specimen immediately after collection. Accurate specimen labeling is essential, as a mismatch between the sample and the accompanying paperwork, which includes the patient’s clinical history, can lead to diagnostic errors. The tissue must be transported quickly to the laboratory while maintaining its integrity.
Upon arrival, the tissue undergoes fixation, a chemical process that preserves cellular structures by immersing the sample in a solution, typically 10% neutral buffered formalin. Fixation halts the natural degradation of the tissue, preparing it for later examination. Adequate fixation time is necessary for the solution to penetrate the entire specimen.
The gross examination, or “grossing,” follows fixation and involves visually inspecting and describing the specimen. This step includes documenting the size, color, and any visible abnormalities. For larger surgical specimens, the professional dissects the tissue and selects representative areas, placing these small fragments into labeled plastic cassettes for further processing.
Transforming Tissue into a Viewable Slide
The next phase is the technical process of preparing the tissue fragments for microscopic viewing, transforming the soft biological material into a hard block that can be thinly sliced. Tissue processing begins with dehydration, where water is removed using progressively higher concentrations of alcohol. A clearing agent like xylene is then used to remove the alcohol, as it does not mix with the embedding medium.
Following clearing, the tissue is infiltrated with molten paraffin wax, which fills all the empty spaces within the tissue structure. This step provides the tissue with the firm support it needs to withstand sectioning. The wax-infiltrated tissue is placed into a mold, along with the identifying cassette, and cooled to solidify, resulting in a hard paraffin block.
The hardened block is taken to a microtome, a precision instrument used to cut the tissue into extremely thin sections, typically measuring between four and five micrometers thick. This thickness allows light to pass through the tissue for examination under a microscope. The thin sections are floated onto a warm water bath to flatten them before being mounted onto glass slides.
The mounted tissue sections are then subjected to the routine Hematoxylin and Eosin (H&E) stain, which provides the basic contrast needed to see cellular structures. Hematoxylin stains the cell nuclei a blue-purple color. Eosin stains the cytoplasm and extracellular matrix pink, providing a general overview of the tissue architecture and morphology.
The Pathologist’s Role in Interpretation and Reporting
The analytical phase begins once the slide is prepared, as the pathologist performs a microscopic examination to translate the visual findings into a clinical diagnosis. The pathologist scans the H&E-stained slide, observing the size, shape, and arrangement of the cells and the overall tissue pattern. They look for subtle changes that indicate disease, such as abnormal cellular growth or structural disorganization.
The pathologist correlates the visual evidence on the slide with the clinical history provided by the treating physician. This synthesis of information, which may include details about the patient’s symptoms or previous test results, ensures an accurate and contextually relevant diagnosis. For cancer cases, the pathologist determines the specific tumor type and assigns a grade based on cellular abnormality and growth rate.
The final output is the diagnostic report, a formal document delivered to the treating clinician. This report includes a detailed description of the gross specimen and the microscopic findings, culminating in a definitive diagnosis. The report serves as the official record of the disease, guiding subsequent decisions regarding patient treatment and management.
Ensuring Accuracy Through Specialized Testing and Quality Control
After the initial H&E diagnosis, specialized testing may be performed to confirm findings, distinguish between similar diseases, or provide predictive information for treatment. These specialized tests provide supplementary data that builds upon the foundational H&E diagnosis.
Immunohistochemistry (IHC)
Ancillary testing often includes IHC, a technique that uses antibodies to detect specific proteins or markers on the surface of cells within the tissue. For example, IHC can identify receptor proteins on cancer cells, which helps determine if a patient might respond to targeted therapies.
Molecular Pathology
Molecular pathology is another form of advanced testing that analyzes the genetic material, such as DNA or RNA, within the tissue. This testing can identify specific gene mutations or rearrangements that are driving the disease, offering precise targets for personalized medicine.
Quality Control and Tracking
Throughout the entire process, comprehensive quality control (QC) checks are performed to assure diagnostic reliability. Internal QC involves the consistent calibration of equipment, the monitoring of reagent effectiveness, and the double-checking of complex or difficult cases by a second pathologist. Furthermore, sophisticated Laboratory Information Management Systems (LIMS) are used to track every step of the specimen’s journey, ensuring that the right tissue is always matched with the correct patient data and documentation.