What is the recommended procedure for cholinesterase lab blood sample collection?

Recommended Procedure for Cholinesterase Lab Blood Sample Collection

Blood samples for cholinesterase testing should be processed within 2 hours of collection when kept at room temperature to maintain optimal specimen integrity and testing accuracy. 1

Collection Procedure

Pre-Collection Preparation

• Use appropriate collection tubes based on the specific cholinesterase test being performed
• For plasma cholinesterase (PChE/BChE): Use EDTA or heparin tubes
• For erythrocyte acetylcholinesterase (AChE): Use EDTA tubes
• Ensure tubes are properly labeled before collection

Collection Technique

1. Use 19-21 gauge needles for venipuncture 2
2. Apply tourniquet only long enough to locate a vein (ideally 60 seconds or less) 2
3. Collect at least 5 ml of blood to ensure sufficient specimen for testing 2
4. Fill tubes until vacuum is exhausted 2

Immediate Post-Collection Handling

• For EDTA tubes: Immediately after collection, gently invert/mix the tubes 8-10 times (180-degree turns) 2
• Place tubes upright on a rack until processing 2
• Keep blood at room temperature (not on ice) 2

Sample Processing

Timing Requirements

• Process samples as quickly as possible, ideally within 1 hour of collection 2
• Maximum allowable time from collection to processing: 2 hours at room temperature 1
• If processing must be delayed, refrigerate samples (4°C) for no longer than 2 hours 2
• Avoid direct contact of blood tubes with ice to minimize cell lysis 2

Centrifugation Parameters

• For plasma separation:
  • Centrifuge balanced tubes at 1500-2000 × g for 10 minutes at 4°C 2
  • Use horizontal rotors 2
• For serum (if required):
  • Allow blood to clot for 30-60 minutes at room temperature before centrifugation 2
  • Centrifuge at 1500-2000 × g for 10 minutes at 4°C 2

Sample Transfer and Storage

• Use disposable transfer pipettes to collect plasma/serum 2
• Transfer to appropriate secondary containers (polypropylene recommended to reduce adherence of analytes) 2
• If multiple tubes are collected, combine samples into a single conical tube 2
• Gently invert the conical tube 8-10 times to mix 2
• Aliquot into labeled microtubes or cryovials with O-ring-sealed screw caps 2
• Store all aliquots upright in a specimen box at -80°C or colder 2

Critical Considerations

Avoiding Common Pitfalls

• Do not use pneumatic tube transport systems as they can significantly modify enzyme parameters 2
• Avoid hemolysis as it significantly deteriorates sample quality and is a primary cause of unusable specimens 2
• Prevent contamination with fetal blood when testing amniotic fluid for AChE, as this can lead to false-positive results 2
• Minimize freeze-thaw cycles as they can significantly reduce enzyme activity 1
• For cholinesterase testing specifically, be aware that prolonged exposure to heat can accelerate enzyme degradation 1

Special Considerations for Cholinesterase Testing

• Cholinesterases are sensitive to environmental conditions and proper handling is essential for accurate measurement 3
• For suspected organophosphate or nerve agent exposure cases, rapid processing is particularly critical as these compounds inhibit cholinesterase activity 4
• Activity levels below 10% of normal can be a lethal indicator in cases of anti-cholinesterase insecticide poisoning 5

By following these standardized procedures, laboratories can ensure reliable and accurate cholinesterase testing results that support appropriate clinical decision-making.