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?

Ethanol and Ionized Calcium Testing Cannot Be Added to Previously Processed Samples

You should not add ethanol (ETOH) and ionized calcium tests to a patient sample that was collected 3 hours ago and has already been processed (opened), as this will lead to inaccurate results that could negatively impact patient care. 1

Why These Tests Cannot Be Added to Processed Samples

Ionized Calcium Testing Requirements

• Ionized calcium samples require:
  • Collection in specialized tubes with measured quantities of heparin 1, 2
  • Specific collection protocols to maintain sample integrity 1
  • Protection from air exposure as this alters pH, which directly affects ionized calcium levels 1, 3

Ethanol Testing Requirements

• Ethanol testing samples require:
  • Collection in sodium fluoride/potassium oxalate tubes 1
  • Proper filling to maintain correct blood-to-additive ratio 1
  • Immediate mixing after collection 1
  • Protection from air exposure to prevent evaporation of volatile ethanol 1, 4

Impact of Sample Processing on Test Accuracy

For Ionized Calcium

• Opening tubes alters pH which directly affects ionized calcium levels 1, 2
• Changes in pH can cause falsely decreased or elevated ionized calcium results 1, 5
• Accurate ionized calcium measurement is critical for diagnosing parathyroid disorders, electrolyte imbalances, and managing critically ill patients 1

For Ethanol

• Opening tubes allows evaporation of volatile ethanol 1
• Evaporation leads to falsely decreased ethanol levels 1, 4
• Inaccurate ethanol results can impact toxicology assessment, legal determinations, and medical management 1

Proper Response to the Physician

1. Explain that both tests cannot be added to previously processed samples due to sample integrity concerns
2. Recommend collecting fresh samples in appropriate tubes:
   • For ionized calcium: specialized tubes with measured heparin quantities 1, 2
   • For ethanol: sodium fluoride/potassium oxalate tubes filled to proper height 1
3. Emphasize that using processed samples would lead to inaccurate results that could harm patient care 1
4. Suggest alternative approaches if immediate testing is needed:
   • For calcium assessment: consider total calcium with albumin adjustment if ionized calcium testing cannot be performed immediately 3
   • For ethanol: emphasize that there is no valid alternative to proper collection for accurate results 1

Clinical Significance

• Inaccurate ionized calcium results could lead to inappropriate treatment decisions for critical conditions like hypercalcemia, hypocalcemia, or parathyroid disorders 1
• Inaccurate ethanol results could lead to improper medical management and potentially invalid legal determinations 1
• The normal ionized calcium range is 1.1-1.3 mmol/L, and deviations require accurate measurement for proper intervention 1

Remember that maintaining strict preanalytical standards is essential for laboratory test accuracy and patient safety. Compromising these standards by adding tests to previously processed samples introduces unacceptable risks of inaccurate results.