MLPAO Specimen Processing and Handling Questions and Answers 2 — Questions and Answers

Question 1: What is the maximum acceptable cold ischemia time for a kidney transplant organ from declaration of brain death to organ reperfusion?

2-4 hours
6-12 hours
12-36 hours (Correct answer)
48-72 hours

Correct answer: 12-36 hours

Cold ischemia time for kidneys is generally acceptable up to 24-36 hours with proper cold perfusion preservation, though outcomes improve significantly with shorter times (<12 hours).

Cold ischemia time (CIT) is the duration from when an organ is cooled (by cold perfusion solution) to when blood flow is restored (reperfusion) after transplantation. Acceptable maximum CIT varies by organ: heart and lungs (4-6 hours), liver (12-24 hours), pancreas (12-24 hours), kidneys (24-36 hours). Kidneys tolerate longer cold ischemia due to their physiological adaptations. However, extended CIT increases the risk of delayed graft function. In laboratory practice, understanding organ preservation conditions is relevant when processing biopsies from transplant organs. Tissue banking and organ recovery involve laboratory oversight including typing, crossmatch, and culture specimens that must be processed within defined time windows.

Question 2: A CSF specimen is collected in three tubes. Which tube should be sent to the microbiology laboratory for culture?

Tube 1 — most likely to contain pathogens
Tube 2 — least likely to be contaminated with skin flora (Correct answer)
Tube 3 — largest volume
Any tube may be used for culture

Correct answer: Tube 2 — least likely to be contaminated with skin flora

Tube 2 is sent for microbiology culture because it is least likely to be contaminated with skin flora from the puncture site, which is most likely to contaminate Tube 1.

When CSF is collected by lumbar puncture, three or more sequential tubes are filled. The recommended tube distribution in most Canadian protocols: Tube 1 → Biochemistry (protein, glucose, LDH) or hold; Tube 2 → Microbiology (culture and sensitivity, Gram stain); Tube 3 → Hematology (cell count, differential). Tube 1 is most likely to contain blood from a traumatic tap (contaminated with skin flora from the needle path). Tube 3 is sent to hematology for cell count to compare with Tube 1 — if Tube 1 has more RBCs than Tube 3, this suggests a traumatic tap rather than true subarachnoid hemorrhage. Tube 2 is the cleanest specimen for culture. CSF must be processed immediately (never refrigerated for culture or cell count).

Question 3: A laboratory receives a serum specimen for cortisol measurement labeled 'AM cortisol — 0900 hours.' The specimen was collected at 0900 but not processed until 1600. Is this specimen acceptable?

Yes, cortisol is stable in serum at room temperature for 24 hours
No, cortisol may degrade; check stability guidelines and consider recollection if outside stability limits (Correct answer)
Yes, if the specimen has not been centrifuged yet
No, cortisol must always be processed within 30 minutes of collection

Correct answer: No, cortisol may degrade; check stability guidelines and consider recollection if outside stability limits

Cortisol stability should be verified against laboratory stability data. Most guidelines indicate serum cortisol is stable for 4-8 hours at room temperature and longer if refrigerated, but the 7-hour delay warrants stability verification.

Specimen stability is analyte-specific and dependent on temperature, collection tube type, and time since collection. For cortisol: serum is typically stable 4-8 hours at room temperature (15-25°C) and up to 24-48 hours at 2-8°C. A 7-hour delay at room temperature before centrifugation would be at or beyond room-temperature stability limits for many analytes. The appropriate response is to check the laboratory's validated stability guidelines for cortisol: if within acceptable limits, the specimen may be processed; if outside limits, notify the ordering team and request recollection. Cortisol is also subject to diurnal variation — the AM collection time is clinically relevant, making sample timing documentation critical for interpretation.

Question 4: What does 'aliquoting' a specimen mean in laboratory specimen processing?

Discarding excess specimen after analysis
Dividing a primary specimen into smaller portions for multiple tests or storage (Correct answer)
Mixing a specimen by inversion before analysis
Filtering a specimen to remove particulates

Correct answer: Dividing a primary specimen into smaller portions for multiple tests or storage

Aliquoting involves transferring measured portions of a primary specimen into secondary tubes or containers to allow multiple tests to be performed from a single collection or for archival storage.

Aliquoting is a fundamental laboratory specimen management practice. A primary specimen (e.g., primary serum tube) is divided into aliquots — measured portions transferred to labelled secondary tubes — to: (1) Allow multiple different tests requiring the same matrix (serum, plasma) to be performed from a single blood draw, minimizing re-collection; (2) Provide backup specimens if the primary is compromised; (3) Archive specimens for repeat testing, additional reflexive tests, or research. Aliquot labelling must include the patient identifier and, where relevant, the aliquot sequence number. Volume requirements per test must be calculated to ensure adequate primary specimen collection. Aliquot storage conditions (temperature, duration) must match the stability requirements of the intended tests.

Question 5: Which of the following correctly describes the impact of lipemia on clinical chemistry test results?

Lipemia only affects triglyceride measurements
Lipemia causes interference in multiple assays by light scattering, false volume exclusion, and reagent interference (Correct answer)
Lipemia has no significant effect if specimens are centrifuged before analysis
Lipemia only affects colorimetric assays and not immunochemical assays

Correct answer: Lipemia causes interference in multiple assays by light scattering, false volume exclusion, and reagent interference

Lipemia causes multiple interferences: turbidity affects photometric assays (light scatter), lipid particles displace aqueous volume (pseudohyponatremia with indirect ISE), and lipids can interfere with reagent chemistry.

Lipemia (elevated lipids causing turbid plasma/serum) interferes with laboratory tests through multiple mechanisms: (1) Spectrophotometric interference — light scatter increases absorbance readings, particularly at wavelengths 340-700 nm, affecting colorimetric assays (e.g., bilirubin, total protein); (2) Volume displacement (indirect ISE) — lipid particles occupy aqueous phase, causing pseudohyponatremia and pseudohypokalemia with indirect ion-selective electrode methods; (3) Chemical interference — lipids can extract lipophilic chromogens or precipitate proteins; (4) Optical density interference in nephelometry and turbidimetry. Mitigation strategies include: specimen blanking, centrifugation/ultracentrifugation, sample dilution, or using direct ISE methods. Severely lipemic specimens may require fasting recollection. Serum index reporting (hemolysis, icterus, lipemia indices) is used by modern analyzers to flag these interferences.

Question 6: When storing serum specimens for up to 7 days pending batch analysis, what is the appropriate storage temperature?

Room temperature (15-25°C)
Refrigerator (2-8°C) (Correct answer)
Freezer (-20°C)
Ultra-low freezer (-70°C) for all analytes

Correct answer: Refrigerator (2-8°C)

For short-term storage (up to 7 days), most serum chemistry analytes are stable when refrigerated at 2-8°C. This temperature slows enzymatic degradation and bacterial growth without causing freeze-thaw damage.

Specimen storage temperature requirements vary by analyte and duration: (1) Room temperature (15-25°C) — appropriate for most analytes up to 8 hours after collection/centrifugation; (2) Refrigerator (2-8°C) — appropriate for most common chemistry analytes (electrolytes, enzymes, proteins, hormones) for 24-72 hours and up to 7 days for many; (3) Freezer (-20°C) — for extended storage (>7 days) for most chemistry analytes; (4) Ultra-low freezer (-70°C or -80°C) — required for specific analytes (coagulation studies, proteins C and S, molecular/DNA specimens, some hormones, viral load assays). Some analytes have specific requirements: unstable enzymes (like ALD) degrade at all storage temperatures; others like bilirubin require light protection regardless of temperature.

MLPAO Specimen Processing and Handling Questions and Answers 2

What is the maximum acceptable cold ischemia time for a kidney transplant organ from declaration of brain death to organ reperfusion?