Phlebotomy · Processing · 7 min read
Temperature, Light and Time Requirements
- Identify specific temperature protocols for chilled, warmed, refrigerated, and frozen specimens, including correct ice slurry preparation.
- Describe light-protection procedures and identify key light-sensitive analytes such as bilirubin and porphyrins.
- Explain allowable processing timeframes, cellular glycolysis, clotting requirements, and the phlebotomist's duty to report handling deviations.
Chilled Specimen Handling and Ice Slurry Preparation
Chilling a specimen slows down cellular metabolic processes and preserves analyte stability. When whole blood is collected into an evacuated tube, living cells continue their natural chemical reactions. Cooling the sample slows cellular reactions but does not stop them, so the laboratory's processing time limits still apply. An everyday comparison is placing perishable groceries into an insulated cooler to prevent them from spoiling before you reach home. Before drawing any temperature-sensitive or time-critical specimen, the phlebotomist must always verify patient identification using at least two independent identifiers.
When chilling is designated for a specimen, the phlebotomist must prepare an ice slurry consisting of an equal mixture of crushed ice and water to ensure even cooling around the entire tube. A critical error to avoid is placing a tube directly on solid ice when chilling is required. Solid ice cubes may cool a tube unevenly because they contact only parts of its surface; use an ice-water slurry when the laboratory requires chilling. Uneven cooling may compromise the required handling conditions; exposure to subfreezing materials, such as frozen packs, can freeze a specimen and damage cells.
Specific blood tests require strict adherence to chilling protocols. The phlebotomist must follow the laboratory's ammonia collection instructions, as many protocols require immediate transport in an ice-water slurry and prompt processing. Follow the laboratory's lactate collection instructions as well; some methods require immediate chilling and prompt separation, while others permit rapid transport at room temperature. Collect ACTH in the laboratory-specified tube and follow its transport requirements, which may include immediate chilling. For parathyroid hormone specimens, follow the laboratory's tube, temperature, and processing requirements, noting that immediate chilling is not required by every method. For gastrin, follow the laboratory's specimen instructions, which may require prompt chilling, separation, and freezing. In contrast, transport blood gas specimens collected in plastic syringes promptly at room temperature, chilling them only if the laboratory's protocol specifically requires it.
Common mistakes
- Placing a tube on solid ice cubes instead of using a required ice-water slurry, which can result in uneven cooling.
- Using an infant heel warmer packet to transport warm specimens like cold agglutinins instead of a laboratory-approved, temperature-controlled device calibrated to 37 degrees Celsius.
- Refrigerating sodium citrate tubes for routine coagulation testing, which can alter test results, or freezing whole blood CBC tubes, which causes hemolysis.
- Centrifuging a serum separator tube before it has fully clotted at room temperature, which allows latent fibrin strands to form in the serum.
Key points
- An ice-water slurry provides uniform cooling when chilling is required; solid ice alone provides less consistent contact, and subfreezing materials can damage cells.
- Pre-warm cold agglutinin tubes as instructed and keep specimens requiring warm handling at approximately 37 degrees Celsius until the laboratory-specified separation step; premature cooling can compromise results, including cold agglutinin titers.
- Light-sensitive analytes such as bilirubin and porphyrins must be shielded promptly using amber containers, aluminum foil, or light-blocking transport bags to prevent degradation.
- Serum or plasma must generally be separated within two hours to prevent glycolysis from dropping glucose by 5 to 7 percent per hour at room temperature and to prevent potassium leakage.
- Serum separator tubes must clot completely at room temperature before centrifugation to avoid latent fibrin strands; chilling unclotted tubes inhibits the coagulation cascade.
- Laboratory refrigerators operate at 2 to 8 degrees Celsius, freezers at or below minus 20 degrees Celsius, and whole blood CBC specimens must never be frozen.
- Phlebotomists verify patient identity with two independent identifiers and report any time or temperature deviations to the nurse or supervisor rather than interpreting results.
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Sample lesson: Serum, Plasma and Clotting Before Centrifugation25 practice questions on this exam
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