5.4 Time, Temperature, and Light Handling
Key Takeaways
- Many analytes have strict collection-to-processing windows—know the principle that unstable analytes require rapid separation, ice, or special tubes
- Store and transport at the temperature the test requires: ambient, refrigerated, frozen, or body-temperature—never assume 'fridge is always safer'
- Avoid freeze-thaw cycles unless validated; freezing whole blood often destroys cells and invalidates hematology
- Protect light-sensitive analytes (e.g., bilirubin, porphyrins, some vitamins) with amber tubes or foil; document temperature chain for critical send-outs
5.4 Time, Temperature, and Light Handling
Quick Answer: Specimen stability depends on time, temperature, and sometimes light. Process coagulation, ammonia, lactate, and similar unstable tests within protocol windows; use ice slurry or rapid separation when required. Refrigerate or freeze only when the analyte calls for it. Protect bilirubin and other light-sensitive tests from light. Document handling for critical and send-out assays.
A correctly labeled, non-hemolyzed, right-type tube can still yield a wrong answer if it sits on a counter too long, cooks in a hot courier car, or bakes under fluorescent light. Domain II expects the MLA to apply handling rules from the collection manual—not improvisation.
Exact minutes vary by method and facility. Learn patterns and principles; always follow your laboratory’s current stability tables and CLSI-aligned SOPs.
Why Time Matters: In Vitro Changes After Collection
Once blood leaves the vein, cells continue metabolism and analyte concentrations drift:
- Glucose falls as cells consume it (unless fluoride preservative is used).
- Potassium may rise with refrigeration of unseparated whole blood or with delays/hemolysis.
- Lactate rises with continued glycolysis and poor oxygenation of the sample.
- Ammonia rises rapidly at room temperature from amino acid breakdown and cellular metabolism.
- Coagulation factors can degrade or activate depending on time, temperature, and fill quality.
Principle: Unstable analytes need prompt delivery, prompt centrifugation/separation, and/or special preservatives or ice. When the window is missed, reject or recollect rather than report a number that reflects storage artifact.
Common Time-Sensitive Patterns (Principles + Examples)
Use these as exam-ready patterns; confirm local cutoffs in practice.
| Test / group | Handling principle | Typical pattern (facility-specific) |
|---|---|---|
| Coagulation (PT/aPTT) | Proper fill; limit time before testing/separation | Often tested within hours of collection; some aPTT analytes less stable than PT—follow coag SOP |
| Ammonia | Ice slurry, prompt delivery, rapid separation; avoid fist clenching/delays at draw | Tight window (often ~15–30 minutes to lab processing)—know your lab’s limit |
| Lactate | Gray-top fluoride or ice per protocol; rapid processing | Time-critical; delayed ambient whole blood falsely increases lactate |
| Blood gases | Anaerobic syringe, prompt analysis; ice only per current protocol | Minutes matter; air bubbles ruin values |
| ESR | Timed testing from EDTA sample | Must be set up within method time limit |
| Urine culture | Refrigerate if delayed; preservative tubes extend stability | Room-temp delays → bacterial overgrowth |
| CBC | EDTA stability hours at RT; do not freeze | Delayed samples may show artifact on automated counters |
Teaching point for MLA items: When you see ammonia or lactate, think speed + correct temperature/preservative. When you see coag, think full blue top + timely testing. When you see culture, think time and temperature to limit overgrowth or organism death.
Temperature Categories
| Condition | Meaning | Examples of use |
|---|---|---|
| Room temperature (ambient) | Usually ~20–25 °C; avoid extreme heat/cold | Many routine chemistry SSTs short-term; some coag handling per SOP |
| Refrigerated | ~2–8 °C | Many separated sera for delayed chemistry; urine culture holds; some send-outs |
| Frozen | ≤ −20 °C (or colder, e.g., −70 °C for special send-outs) | Aliquots for delayed special chemistry, certain send-out proteins/viruses per manual |
| Body temperature | ~37 °C | Cold agglutinin workups, some cryoglobulin collections—do not refrigerate |
| Ice slurry | Water–ice mix contacting tube (not dry ice on whole blood unless specified) | Ammonia, lactate, blood gases when protocol requires |
Critical contrasts
- Refrigerating whole blood before separation can falsely increase potassium (and affect other analytes). Separate cells from serum/plasma first when the manual requires it, then refrigerate the aliquot if needed.
- Cryoglobulin and some cold-reactive studies require warm collection and transport—refrigeration precipitates analyte and causes false negatives.
- Frozen storage is for approved matrices (usually cell-free aliquots). Freezing EDTA whole blood lyses cells and destroys CBC utility.
Freeze-Thaw Damage
Each freeze-thaw cycle can:
- Denature proteins and enzymes
- Precipitate analytes
- Lyse residual cells
- Degrade viral titers or labile hormones depending on analyte
Rules of thumb:
- Freeze only when the stability table says freezing is acceptable or required.
- Aliquot before freezing so the primary is not repeatedly thawed for add-ons.
- Thaw controlled (often refrigerator or approved RT thaw), mix gently, and inspect for precipitates/fibrin.
- Do not refreeze unless the SOP explicitly allows a defined number of cycles.
Send-out reference labs often reject samples that arrived thawed when frozen transport was required—or frozen when ambient was required. Packaging and courier choice are part of acceptability.
Light Protection
Some analytes photodegrade:
| Analyte group | Handling |
|---|---|
| Bilirubin (especially neonatal) | Amber tube and/or wrap in foil; limit light exposure |
| Porphyrins | Protect from light during collection and transport |
| Some vitamins (e.g., vitamin A, B vitamins per method) | Light-protected containers as specified |
| Certain drugs | Check manual—some are light-sensitive |
If a bilirubin specimen arrives unprotected after prolonged light exposure, follow rejection or limited-result policy. Prevention is easier than argument: stock amber tubes and foil at collection stations for phototherapy babies and porphyrin studies.
Chain of Temperature Documentation
Critical, legal, and send-out specimens may require a temperature chain of custody or transport log:
- Time collected / time packed / time received
- Device readings (refrigerated shipper, data logger)
- Ice present on arrival (yes/no)
- Any excursion (thaw, overheating) noted and escalated
Examples: quantitative molecular send-outs, certain coagulation special tests, forensic toxicology, and research samples. The MLA’s role is to pack correctly, place loggers when required, inspect on receipt, and document exceptions—not to assume “it felt cold enough.”
Integrated Acceptability Decision
Combine this section with 5.1–5.3:
- Right type and fill?
- Labeled with matching identifiers?
- Quality OK (no hemolysis/clots/QNS as applicable)?
- Within time/temp/light stability?
Any hard failure → reject/recollect or escalate for irreplaceable specimens. Soft failures (slight delay with stable analyte) → process per written stability tables and comments.
Scenario Drill Patterns
- Ammonia drawn, left on counter 2 hours: reject/recollect—ammonia rises in vitro.
- Lactate in plain green top, ambient, delayed: likely invalid; protocol often requires gray top and/or ice and rapid process.
- Neonatal bilirubin in clear tube on windowsill: light degradation risk—follow policy; educate collectors to protect from light.
- CBC frozen “to preserve overnight”: unacceptable—cells destroyed.
- Serum aliquot frozen once for send-out vitamin D (if allowed): may be acceptable per manual; document shipper temperature.
Key Takeaways
- Stability = time + temperature + light rules from the collection manual.
- Ammonia/lactate/gases/coag illustrate rapid-handling principles; know the pattern even when exact minutes are local.
- Fridge and freezer are not universal goods—wrong temperature invalidates (K+, cryoglobulins, whole-blood hematology).
- Protect light-sensitive tests; document the temperature chain for critical and send-out work.
Which handling pattern best matches a correctly collected ammonia specimen?
Why is refrigerating unseparated whole blood before chemistry centrifugation often problematic for potassium?
A neonatal total bilirubin specimen was transported in a clear tube exposed to bright light for an extended period. What is the primary concern?
A collector freezes an EDTA whole-blood CBC tube overnight 'to keep it fresh.' What should processing staff do?