The pathology workflow describes the systematic journey a tissue or fluid sample takes from its initial collection to the final diagnostic report. This intricate process involves multiple precise steps carried out by healthcare professionals within a specialized laboratory. Understanding this progression highlights how samples are meticulously handled and analyzed to provide accurate information, directly contributing to informed medical decisions and effective patient care.
From Patient to Lab: Sample Handling
The pathology workflow begins with sample collection from a patient, using methods like surgical biopsy, organ removal, or fluid aspiration. Once collected, the sample is immediately placed into a container and labeled with patient identifiers and clinical details. This labeling ensures the sample is correctly associated with the patient.
Following collection, tissue samples undergo fixation, often in 10% neutral buffered formalin. This chemical process stabilizes cellular and tissue structures, preventing degradation and preserving them for analysis. Proper fixation is time-sensitive, requiring the sample to remain in formalin for a specific duration, typically 6 to 72 hours, depending on size and type.
A pathologist or pathology assistant then performs a gross examination, a macroscopic visual inspection of the specimen. During this step, the sample’s size, shape, color, and any visible abnormalities are documented. Specific areas for microscopic examination are selected and sectioned, then placed into small, labeled plastic cassettes, preparing them for processing.
The Diagnostic Core: Analyzing Samples
Once samples arrive in the laboratory in their labeled cassettes, they undergo processing steps to prepare them for microscopic examination. Tissue pieces are first subjected to dehydration, passing them through increasing concentrations of alcohol to remove water. Following dehydration, a clearing agent, such as xylene, removes alcohol and prepares the tissue for paraffin wax infiltration.
The cleared tissue is then embedded into a block of molten paraffin wax, which solidifies upon cooling, providing structural support. This paraffin block is mounted onto a microtome, a specialized instrument that cuts the tissue into thin sections, typically 3 to 5 micrometers. These sections are floated onto a water bath to flatten them before being picked up onto glass slides.
Next, thin tissue sections are stained to make cellular components visible under a microscope, as unstained tissue is transparent. Hematoxylin and Eosin (H&E) staining is the most common method; hematoxylin stains cell nuclei blue, and eosin stains the cytoplasm and extracellular matrix pink. This differential staining allows pathologists to distinguish cell types and tissue structures, identifying architectural changes or cellular abnormalities.
A pathologist examines the stained slides under a microscope, scrutinizing cellular morphology and tissue architecture. They search for deviations from normal, such as abnormal cell growth, inflammation, or foreign material, correlating findings with the patient’s clinical history. For complex cases or to confirm a diagnosis, advanced techniques like immunohistochemistry (detecting specific proteins with antibodies) or molecular testing (analyzing DNA or RNA) may provide additional diagnostic clarity.
Delivering Results: Reporting and Archiving
Following microscopic examination, the pathologist synthesizes all findings (gross description, microscopic observations, ancillary test results) to formulate a diagnosis. This diagnosis is documented in a formal pathology report, serving as a comprehensive record of the specimen’s analysis. The report includes patient demographics, specimen description, microscopic findings, and the final diagnosis, sometimes with additional comments.
The completed pathology report is communicated to the referring physician, often through secure electronic systems or direct phone call. This timely communication ensures the clinician has information to discuss the diagnosis with the patient and determine treatment. The report becomes part of the patient’s medical record, guiding future clinical decisions.
Beyond reporting, the physical tissue blocks and glass slides are archived within the pathology department. Paraffin blocks, being stable, can be stored for many years, often for 10 to 20 years or indefinitely. This archiving allows for future re-examination, additional testing if needed, or serves as a resource for medical education and research, preserving a record of the diagnosis.
Ensuring Accuracy: Quality Control
Maintaining the reliability of pathology results is achieved through a comprehensive system of quality control and assurance (QC/QA) measures throughout the workflow. Laboratories regularly calibrate and maintain equipment, from tissue processors to microscopes, to ensure they function within specifications. This minimizes technical errors that could affect sample processing or image clarity.
Staff training and adherence to standardized operating procedures (SOPs) are emphasized. Each workflow step, from sample accessioning to microscopic examination, is guided by protocols, ensuring consistency and reproducibility of results across cases and personnel. Competency assessments are regularly conducted to confirm staff are proficient in their tasks.
Laboratories participate in both internal quality control checks and external proficiency testing programs. Internal checks involve reviewing a percentage of cases or re-examining slides to confirm diagnoses. External programs involve analyzing unknown samples from an independent organization, with results compared against a consensus diagnosis, validating the laboratory’s diagnostic accuracy against broader standards. This approach to quality control underpins the trustworthiness of pathology diagnoses, directly supporting patient safety and effective medical care.