8.2 Time, Temperature & Special Requirements

Domain II-B tests whether you can recognize specimens that are not "draw, bag, and send at room temperature." Some analytes change within minutes if the tube sits warm on a counter; others precipitate if the tube gets cold; still others photodegrade under fluorescent lights. Timed therapeutic drug levels and legal specimens add scheduling and documentation requirements on top of chemistry stability. Master the categories—cold, body temperature, light-protected, timed, and chain of custody—and then memorize the classic examples the RPT exam loves: ammonia, lactate, bilirubin, and cryoglobulin.

Chilled (Cold) Specimens

Chilling slows cellular metabolism and enzymatic activity that would otherwise alter analyte concentrations after the blood leaves the vein. The usual bedside method is an ice slurry (ice and water mixed so the tube is surrounded by cold liquid contact), not a handful of dry ice and not a tube perched on top of a few cubes with air gaps.

High-yield chilled analytes:

Practical chilled-specimen technique:

• Pre-label and prepare the ice slurry before the stick so the tube or syringe goes on ice within seconds.
• Do not freeze the specimen solid unless the laboratory orders frozen transport after processing—whole-blood freezing lyses cells and ruins many assays.
• Keep the specimen moving. "On ice" is not permission to leave it in a nursing-station bucket for an hour.
• For ABGs, remove air bubbles promptly; air in the syringe alters PO₂/PCO₂. Confirm whether your facility still ices all ABGs or uses room-temperature rapid analysis with modern analyzers—follow current local SOP, but know the classic exam answer that ABGs are handled as chilled, time-critical specimens.

Opposite trap: Potassium is generally not shipped on ice for routine chemistry because cold can cause falsely elevated potassium as cells leak. Do not ice "everything STAT."

Body-Temperature (Warmed) Specimens

Some specimens must stay near body temperature (≈37°C) from collection through initial clotting or separation. Cooling allows cryoproteins or cold-reactive antibodies to bind or precipitate, falsely lowering measured levels in the serum you eventually submit.

Classic body-temperature specimens:

• Cryoglobulins — immunoglobulins that precipitate in the cold. Collect into a prewarmed tube, keep in a heel warmer, 37°C heat block, or warm-water transport system, and deliver promptly so the laboratory can clot and separate at warm temperature.
• Cold agglutinins — antibodies that agglutinate RBCs below body temperature. Keep the specimen warm until serum is separated; chilling the whole-blood tube can trap antibody on cells and falsely lower the titer measured in serum.

Warming does not mean placing tubes on a radiator until they cook, and it does not mean microwaving. Use validated warm packs or incubators supplied by the laboratory. Never confuse cryoglobulin (keep at body temperature) with cryofibrinogen protocols that may have related but not identical handling—read the test directory.

Light-Protected Specimens

Light—especially fluorescent and sunlight—breaks down certain analytes. Protection usually means wrapping the tube in aluminum foil, using an amber tube, or placing the specimen in a light-blocking transport bag immediately after collection.

Common light-sensitive examples:

If you draw bilirubin and leave the tube uncovered under bright lights while finishing other paperwork, you can produce a falsely low result that misguides evaluation of jaundice. Protect first, then finish logistics.

Timed Specimens

A timed specimen can have the perfect tube and still be worthless if the clock is wrong. Domain II-B overlaps with time-management competencies, but you must know the integrity angle here: documented collection time is part of the result.

Examples:

• Therapeutic drug monitoring (TDM): Trough levels are usually drawn immediately before the next dose; peak timing depends on the drug and route (e.g., a timed interval after IV infusion). Drawing "whenever you pass the room" creates falsely high or low levels and dangerous dose changes.
• Glucose tolerance tests (GTT): Baseline fasting draw, timed glucose beverage, then draws at prescribed intervals (commonly 1 hour, 2 hours, etc.). Starting the clock late or missing a draw invalidates the curve.
• Diurnal hormones (e.g., cortisol): Morning vs evening values differ physiologically; wrong-time collection misclassifies adrenal status.
• 2-hour postprandial glucose: Timing begins with the meal (or test drink), not when you arrive on the floor.

Always record actual clock time. If the dose was given late, notify nursing/pharmacy and document—do not silently relabel a late draw as "trough."

Chain of Custody and Legal Specimens

Chain of custody (COC) is the paper (or electronic) trail proving who handled a specimen from collection through reporting when results may be used for legal, employment, or forensic decisions. Blood alcohol for legal purposes, workplace drug screens, and certain toxicology collections fall here.

Integrity + legal requirements typically include:

• Positive patient identification and often photo ID for non-patient workplace collections
• Tamper-evident seals applied in view of the donor/patient
• COC form with date, time, and signature of each person who takes possession
• Restricted access—no undocumented "I'll just run this to the lab for you" handoff
• For legal blood alcohol: cleanse the site with non-alcohol antiseptic (e.g., soap and water, benzalkonium, or povidone-iodine per protocol)—alcohol pads can be challenged as contaminating the specimen
• Fill tubes adequately; headspace can allow volatile alcohol loss in some collection systems

Chain of custody is not required for every ammonia or bilirubin tube. Use it when the order or facility policy designates the specimen as legal/forensic/employment testing.

Putting Special Handling on One Card

Exam Traps

• Icing a cryoglobulin specimen "to keep it fresh" destroys the test.
• Warming an ammonia tube in a pocket while you finish rounds lets ammonia climb.
• Drawing a vancomycin trough 2 hours after the dose because the patient was at X-ray produces a falsely elevated "trough."
• Using an alcohol pad for a legal blood alcohol draw creates a defensibility nightmare even if the chemistry result looks precise.

Special requirements are not optional customer service—they are part of the preanalytical method. If you cannot meet the temperature, light, time, or custody requirement, escalate before you stick, or recollect rather than submit a specimen you already know is compromised.