Specimen Processing and Handling
Core concepts
Collection is only half the job; specimen integrity after the draw drives most processing questions. Know which tubes need immediate mixing: invert gently 3–10 times depending on additive (EDTA and heparin tubes need thorough but gentle inversion; never shake, which hemolyzes red cells and releases potassium and hemoglobin). Serum and plasma tubes are centrifuged under validated speed and time to separate cells from liquid; gel separator tubes must not be recentrifuged.
Temperature and timing matter. Light-sensitive analytes (bilirubin, some vitamins) require amber protection. Ammonia, lactate, and blood gases require iced transport and rapid delivery. Coagulation testing is time-sensitive and should be transported and processed promptly per facility protocol. Serum and plasma for routine chemistry may be held refrigerated if not tested quickly, but whole blood for hematology should not be refrigerated unless the test requires it.
Rejection criteria are high-yield: unlabeled or mislabeled tubes, hemolyzed samples for potassium or LDH, clotted samples in anticoagulant tubes, short draws in citrate tubes that alter the blood-to-additive ratio, and expired collection devices. A specimen that arrives without proper labeling must be rejected and recollected; do not "fix" the label after the fact.
Worked example
A lavender tube arrives clotted and the order is a CBC. Because the EDTA did not mix or the draw was difficult, the sample is unsuitable. The correct action is to reject it and recollect, not to run it and comment.
Rule of thumb: if the tube's additive and the test's analyte conflict (EDTA for calcium, heparin for coagulation), the specimen is wrong regardless of how well it was handled.