Study guide
5.4 Time, Temperature, and Light Handling
ASCP Medical Laboratory Assistant MLA
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1 Introduction & Exam Overview
1.1 About the ASCP MLA Exam 1.2 Eligibility Routes and Study Plan
2 Chapter 2: Orders, Identification & Communication
2.1 Review, Clarification, and Verification of Test Orders 2.2 Patient Identification 2.3 Patient Communication
3 Chapter 3: Collection Procedures
3.1 Patient Assessment and Preparation 3.2 Site Selection 3.3 Tubes, Anticoagulants, and Order of Draw 3.4 Specimen Types for Common Tests
4 Chapter 4: Special Collections, Reactions & Handling
4.1 Special Collection Procedures 4.2 Adverse Collection Reactions 4.3 Specimen Labeling and Immediate Handling
5 Chapter 5: Specimen Acceptability Assessment
5.1 Correct Specimen Type for the Test 5.2 Specimen Quality Assessment 5.3 Labeling Requirements and Rejection Criteria 5.4 Time, Temperature, and Light Handling
6 Chapter 6: Add-on Requests & Special Specimen Types
6.1 Specimen Suitability for Add-on Requests 6.2 Special Specimen Types
7 Chapter 7: Prioritization, Distribution & Transport
7.1 Department Distribution and Prioritization 7.2 Pneumatic Tube System 7.3 External Packaging and Shipment
8 Chapter 8: Specimen Processing Techniques
8.1 Centrifugation 8.2 Aliquoting 8.3 Non-Blood Specimen Processing 8.4 Microbiology Setup and Plating
9 Chapter 9: Slide Preparation & Specimen Storage
9.1 Slide Preparation 9.2 Specimen Storage (Pre- and Post-Testing)
10 Chapter 10: Reagents, Instrumentation & Quality Control
10.1 Reagents, Standards, and Controls 10.2 Analytical Instrumentation 10.3 Quality Control
11 Chapter 11: Critical Values, Results & Inventory
11.1 Critical Value Notification and Documentation 11.2 Result Retrieval and Review 11.3 Inventory Management
12 Chapter 12: Waived & Point-of-Care Testing
12.1 Waived and POC Instrument Operation 12.2 Waived/POC QC, Result Evaluation & Reporting
13 Chapter 13: Laboratory Regulations, Chemical & Fire Safety
13.1 Laboratory Regulations 13.2 Chemical Safety 13.3 Fire Safety
14 Chapter 14: Infection Control & Waste Disposal
14.1 Standard Precautions, PPE & Hand Hygiene 14.2 Biological Safety Cabinets, Sharps & Exposure Control 14.3 Biological and Hazardous Waste Disposal
15 Chapter 15: Equipment, Ethics, LIS & Quality Assurance
15.1 Laboratory Equipment Maintenance 15.2 Professionalism, Ethics & HIPAA 15.3 Laboratory Information System (LIS) Functions 15.4 Quality Assurance and Improvement
5.4 Time, Temperature, and Light Handling
Key Takeaways Explain This Topic AI
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
Last updated: August 2026
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.