Which blood specimens should be immediately placed in ice after collection to prevent alterations in concentration?

Blood Specimens That Should Be Immediately Placed on Ice After Collection

Blood specimens for ammonia and lactate should be immediately placed on ice after collection to prevent falsely elevated results due to ongoing metabolic activity in the sample.

Why Immediate Icing is Critical for Ammonia and Lactate

Ammonia

• In vitro deamination generates ammonia in freshly collected blood specimens, causing falsely elevated results 1
• When blood samples are kept at room temperature, ammonia levels can increase significantly:
  • Samples with normal enzyme levels: increase of 0.5 μmol/L/hour at 4°C
  • Samples with elevated ALT/GGT: increase of 3.6 μmol/L/hour at 4°C 1
• Placing specimens on ice immediately after collection significantly reduces this increase 2
• The delay between sampling and analysis should be kept within 2 hours 3

Lactate

• Blood samples kept at room temperature (22-24°C) show an increase in lactate concentration of 0.008 mmol/L/minute 4
• Placing tubes on crushed ice effectively controls glycolysis and lactate production (0.033 mmol/L/hour on ice vs. 0.32 mmol/L/hour at room temperature) 5
• HIV patients show even faster lactate increases at room temperature compared to controls 5
• A clinically significant change (≥0.4 mmol/L) occurs after just 45 minutes at room temperature 4

Processing Recommendations for Ammonia and Lactate

Ammonia Samples

• Place blood collection tubes immediately on ice after collection 2
• Process within 2 hours of collection 3
• Centrifuge at 4°C to retard enzymatic activity 3
• Separate plasma from cells immediately after centrifugation 6
• For longer storage, freeze plasma at -80°C 1

Lactate Samples

• Place blood collection tubes on crushed ice immediately after collection 5
• Avoid direct contact of blood tubes with ice to minimize cell lysis 7
• Samples remain stable for up to 90 minutes when kept on ice 4
• Placing tubes on crushed ice also preserves pH and anion gap 5

Common Pitfalls and Caveats

1. Delayed icing: Even brief delays in placing specimens on ice can lead to falsely elevated results
2. Prolonged storage: Even when refrigerated, samples should be processed within 2 hours 7
3. Venous stasis: Prolonged tourniquet application (>2 minutes) can artificially increase lactate levels 5
4. Multiple freeze-thaw cycles: These significantly reduce enzyme activity and affect results 7
5. Improper centrifugation: Failure to centrifuge at cold temperatures can lead to continued metabolic activity 3

Specimens That Do NOT Require Immediate Icing

• Cholesterol and triglycerides: Can be collected in standard tubes and processed within standard timeframes
• Cortisol and glucose: Do not require immediate icing; standard processing is sufficient
• Calcium and phosphorus: Can be processed at room temperature within standard timeframes

The critical distinction is that ammonia and lactate are highly unstable analytes affected by ongoing cellular metabolism in the sample, while the other listed analytes are relatively stable at room temperature for the typical processing timeframe.