Specimen processing is the systematic sequence of steps that transforms a raw patient sample into a format ready for laboratory analysis. This activity occurs during the pre-analytical phase, linking sample collection with placement on an analyzer. The process is designed to maintain the sample’s integrity, ensuring the specimen accurately reflects the patient’s condition. Errors at this stage can lead directly to inaccurate test results, potentially affecting medical decisions.
Verification and Accessioning
Verification and accessioning begin the moment a specimen arrives in the laboratory. Verification involves checking the sample container label against the accompanying test requisition form. Lab personnel confirm that identifiers, such as the patient’s name and date of birth, match and that the sample type is appropriate for the tests ordered.
Accessioning formally logs the sample into the laboratory information system (LIS). The sample is assigned a unique, traceable laboratory identification number, often via a barcode. This unique ID links the physical sample to all electronic data, including collection time, tests requested, and final results.
This administrative review prevents errors from progressing into the testing workflow. Specimens that are mislabeled, collected in the wrong container, or have insufficient volume for testing (referred to as QNS) are typically rejected. Rejecting a compromised sample prevents the delivery of unreliable data.
Essential Sample Preparation Techniques
After verification, the physical manipulation of the sample begins to make it suitable for analytical instruments. One of the most common techniques is centrifugation, which spins liquid samples at high speeds, separating components based on density. This action forces cellular elements, such as red and white blood cells, to the bottom of the tube, leaving the cell-free liquid portion—serum or plasma—on top.
Separation is necessary because many clinical assays are performed on the liquid component, and cellular matter can interfere with the analysis or consume analytes over time. The resulting serum or plasma is often subjected to aliquotting, dividing the original sample into smaller, secondary tubes. These aliquots are labeled with the unique accession number and may be sent to specialized testing areas or reserved for future add-on tests.
Preparation for solid samples, such as tissue biopsies, differs. Tissues are often placed in a chemical fixative, like formalin, to prevent degradation and preserve cellular structures. For molecular or enzyme analyses, the tissue may be flash-frozen to maintain component stability. These preserved tissues are eventually embedded in a medium like paraffin wax, allowing them to be cut into thin sections for microscopic analysis.
Maintaining Integrity During Processing and Storage
Maintaining the chemical stability of a sample is essential during processing and storage. Many analytes are temperature-sensitive and must be handled under controlled conditions to prevent degradation. Some samples require refrigeration (typically between 2 to 8 degrees Celsius) to slow down metabolic processes that could alter test results.
Other analytes, like certain enzymes or genetic material, require immediate freezing, often at temperatures below -20 degrees Celsius, for long-term preservation. A breach in the required temperature range can cause chemical changes, such as the breakdown of glucose in a blood sample, leading to a falsely low result. Protection from environmental factors also plays a role, as light-sensitive compounds like bilirubin must be shielded to prevent photodecomposition.
Time constraints are equally important, as samples often need to be processed within a specific window after collection to prevent chemical changes. This time-sensitive nature is a major factor in determining the required turnaround time (TAT) for laboratory results. After testing is complete, the samples are typically stored for a defined period, allowing the laboratory to perform repeat or additional testing if requested by a physician.