Temperature: chill it, warm it, or shield it.

Some analytes change the moment they leave the vein. The chill list, the warm list, and the protect-from-light list, with the reasons that make them stick.

Why this matters

Some analytes start changing the moment they leave the vein. The lab depends on you to hold the specimen at the right temperature until it is processed, and the ASCP BOC tests this under specimen handling. The good news: a few short lists cover almost every question, and each has a reason that makes it stick.

Key takeaways

• Room temperature is the default. Most specimens travel and wait at ambient temperature until they are separated.
• Chill these on an ice-water slurry. Ammonia, lactate, pyruvate, and blood gases keep metabolizing in the tube, and cold slows it. Blood gas goes on ice only in a glass syringe or when analysis is delayed; a plastic syringe read within about 30 minutes stays at room temperature, because icing it falsely raises the oxygen reading.
• Keep these warm at 37 C from draw through separation. Cold agglutinins, cryoglobulins, and cryofibrinogen drop out of solution when cold and are lost from the serum, so they ride in a warmed transport.
• Protect these from light. Bilirubin, vitamin B12, folate, and carotene degrade in light. Use an amber tube or wrap the tube in foil.
• Do not refrigerate whole blood before separating it for potassium. Cold makes the cells leak potassium and falsely raises the result. This is the cold mirror of the two-hour separation delay.
• When in doubt, follow your lab's validated table. Test menus vary; the categories above are the reliably tested ones.

Standards reference: CLSI GP44, Handling and Processing of Blood Specimens, with venous collection per CLSI GP41-Ed7. Cross-referenced against the ASCP BOC PBT content guideline. Always follow your own laboratory's validated handling protocol. PhlebotomySkills.com is exam-preparation content. Not a degree, not for-credit coursework, and not affiliated with any certifying body.