What is the significance of a mildly elevated serum lactate (lactic acidemia) level of 2.8 mmol/L in a 4-month-old infant, obtained during a stressful venous draw?

Mildly Elevated Serum Lactate in a 4-Month-Old: Likely Due to Crying During Blood Draw

A serum lactate of 2.8 mmol/L in a 4-month-old infant who was crying and moving during a venous blood draw is most likely a false elevation due to collection circumstances and does not warrant further diagnostic workup in an otherwise well-appearing infant.

Understanding Lactate Elevations in Infants

Normal vs. Abnormal Lactate Values

• A lactate level of 2.8 mmol/L is only mildly elevated
• According to pediatric guidelines, lactate levels >2 mmol/L are common in infants during blood draws 1
• Davies and Gupta found that 54% of infants had lactate levels >2 mmol/L during evaluation, but only 15% had levels >3 mmol/L 1
• Levels >3 mmol/L are more likely to be clinically significant and less likely to represent false positives

Impact of Collection Circumstances

• Crying and movement during blood collection are well-known causes of falsely elevated lactate levels
• Muscle activity during crying and struggling increases lactate production
• Venous stasis from difficult draws can further elevate lactate readings
• These pre-analytical factors are particularly important in infants who cannot cooperate during blood draws

Clinical Decision Making

When to Be Concerned

A lactate level should raise concern when:

• It exceeds 3 mmol/L (more specific for pathology) 1
• It is accompanied by other signs of poor perfusion or illness
• It persists or increases on repeat measurement
• The infant has risk factors for inborn errors of metabolism

When Further Evaluation Is Warranted

Consider additional workup only if:

1. The infant appears ill or has abnormal vital signs
2. There is a family history of inborn errors of metabolism (IEM)
3. The infant has developmental concerns or regression
4. There are recurrent unexplained episodes of lethargy, vomiting, or altered mental status
5. The lactate remains elevated on repeat measurement under optimal collection conditions

Recommendations for Management

Immediate Actions

• If the infant appears well with normal vital signs, no immediate action is needed
• Avoid unnecessary testing that could lead to false positives and parental anxiety

Follow-up Considerations

• If clinical concern exists, consider repeating the lactate measurement under optimal conditions:
  • Ensure the infant is calm and comfortable
  • Use topical anesthetics to minimize pain and struggling
  • Ensure proper collection technique without prolonged tourniquet use
  • Process the sample immediately

Monitoring for Trends

• In pediatric critical care, trends in lactate levels are more valuable than single measurements 1
• The Surviving Sepsis Campaign guidelines suggest using trends in blood lactate levels to guide resuscitation in children with septic shock 1
• A rapidly increasing lactate (>0.6 mmol/L/hour) is more concerning than a stable mild elevation 2

Common Pitfalls to Avoid

1. Overreaction to mildly elevated values: A lactate of 2.8 mmol/L in an otherwise healthy infant with a difficult blood draw is likely a false positive
2. Failure to consider collection circumstances: Crying, struggling, and poor collection technique can all elevate lactate
3. Unnecessary workup: Extensive metabolic testing in well-appearing infants with mildly elevated lactate can lead to more false positives and parental anxiety
4. Ignoring true pathology: While most mild elevations in this context are benign, persistent or increasing lactate levels should not be dismissed

Conclusion

In the context of a crying, moving infant during a venous blood draw, a lactate of 2.8 mmol/L is most likely a false elevation related to collection circumstances. Guidelines indicate that lactate levels >2 mmol/L are common findings in infants during evaluation, with levels >3 mmol/L being more specific for pathology 1. Unless there are other concerning clinical features or risk factors, this finding alone does not warrant extensive metabolic workup or intervention.