Specimen Processing and Preparation
From accession to aliquot
Processing begins at accessioning: verify the requisition matches the label, assign an accession number, and record receipt time and condition. Reject mislabeled, unlabeled, hemolyzed, clotted, or improperly transported specimens according to policy, and document the rejection and notification.
Centrifugation separates cells from serum or plasma. Understand the difference between RPM and relative centrifugal force (RCF/g); only RCF is comparable between centrifuges. Balance tubes opposite each other, use the correct brake setting, and follow the time and speed validated for the tube type. Serum tubes need about 30 minutes to clot at room temperature before spinning; spinning too soon produces fibrin that clogs analyzers.
Gel separator tubes create a barrier; do not recentrifuge aliquots or disturb the barrier. Pour off or aliquot into labeled secondary tubes with two identifiers, specimen type, date/time, and your initials. Store at the temperature the test requires-room temperature, refrigerated, or frozen-and protect light-sensitive analytes (bilirubin, vitamin B12) with foil.
Stability is test-specific: ammonia and blood gases must be transported on ice and analyzed quickly; coagulation testing is stable for a limited time at room temperature. Lipemia, icterus, and hemolysis interfere with many photometric assays and may require a comment or recollection.
Traps: treating RPM as g, centrifuging before a clot forms, or freezing a tube meant for refrigeration (which can hemolyze cells). Rule of thumb: if the result will guide immediate therapy, process and deliver it first.