Can I add ethanol (ETOH) and ionized calcium tests to a patient's sample that was collected 3 hours ago and has already been processed?

Response to Request for ETOH and Ionized Calcium Testing on Processed Samples

You should not add ethanol (ETOH) or ionized calcium tests to samples that were collected 3 hours ago and have already been processed (opened), as this would yield inaccurate results that could negatively impact patient care.

Rationale for Rejecting the Request

Ionized Calcium Testing Considerations:

• Ionized calcium measurement requires proper sample handling to maintain accuracy:
  • Samples for ionized calcium must be collected in specialized tubes with measured quantities of heparin 1
  • Opening tubes alters the sample pH, which directly affects ionized calcium levels 2
  • The American Journal of Kidney Diseases recommends specific collection protocols for accurate ionized calcium measurement 3

Ethanol (ETOH) Testing Considerations:

• Ethanol testing has strict preanalytical requirements:
  • Blood should be collected in proper tubes (typically sodium fluoride/potassium oxalate tubes) 2
  • Tubes must be filled to the proper height to maintain the correct blood-to-additive ratio 2
  • Proper mixing immediately after collection is essential 2
  • Ethanol is volatile and can evaporate from opened specimens 2

Critical Issues with Using Processed Samples:

1. Sample integrity compromised: Once tubes are opened, the original composition is altered through:

   • Exposure to air affecting pH
   • Potential evaporation of volatile substances like ethanol
   • Disruption of the blood-to-additive ratio

2. Risk of inaccurate results:

   • Ethanol levels may be falsely decreased due to evaporation
   • Ionized calcium results would be unreliable due to pH changes and improper collection tubes

Recommended Course of Action

1. Recommend new sample collection:

   • Explain to the physician that new samples must be collected using appropriate tubes:
     • For ionized calcium: Collect in specialized heparinized tubes with measured quantities of heparin 1
     • For ethanol: Collect in sodium fluoride/potassium oxalate tubes (glycolytic inhibitor tubes) 2

2. Proper sample handling:

   • Follow proper order of draw: blood culture → sodium citrate → serum → heparin → EDTA → sodium fluoride/potassium oxalate 2
   • Fill tubes to recommended height to maintain proper blood-to-additive ratio 2
   • Invert tubes immediately after collection according to manufacturer recommendations 2
   • Process samples promptly according to laboratory protocols

3. Documentation:

   • Document the rejection of the add-on request and the rationale
   • Record the recommendation for recollection

Clinical Importance

Accurate ionized calcium and ethanol measurements are critical for proper patient management:

• Ionized calcium is the physiologically active form of calcium and essential for diagnosis of parathyroid disorders, electrolyte imbalances, and critical care management 3, 4
• Ethanol levels are crucial for toxicology assessment, legal determinations, and medical management 2

Providing inaccurate results could lead to inappropriate clinical decisions and potentially harm the patient, which is why maintaining strict preanalytical standards is essential.