How to measure lactate level

How to Measure Lactate Levels

Blood lactate should be measured using either arterial or venous blood samples, with point-of-care testing devices providing rapid results that correlate well with central laboratory analyzers for most clinical applications. 1

Blood Sample Collection Options

• Arterial blood: Gold standard for lactate measurement, especially in critically ill patients 1

  • Collected via arterial puncture or from indwelling arterial catheters
  • Provides the most accurate assessment of tissue hypoperfusion

• Venous blood: Acceptable alternative when arterial access is difficult 1, 2

  • Central venous samples show excellent correlation with arterial samples (correlation coefficient 0.992) 2
  • Peripheral venous samples may show slightly higher values but remain clinically useful

• Capillary blood: Viable option for rapid assessment 2, 3

  • Collected via finger-stick using a lancet
  • Shows strong correlation with arterial values (correlation coefficient 0.945) 2
  • May read slightly higher than arterial values (mean difference ~0.99 mmol/L) 3
  • Caution with values >8 mmol/L, which may be less reliable 4

Measurement Methods

1. Point-of-Care Testing (POCT)

• Handheld analyzers (e.g., i-STAT, Accutrend Plus)
  • Provide rapid results (typically <2 minutes)
  • Allow bedside testing without laboratory delays
  • Show good correlation with central laboratory methods 4, 5
  • Particularly useful in emergency and critical care settings

2. Central Laboratory Analysis

• Standard blood gas analyzers or biochemistry analyzers
• More precise but involves transportation time and processing delays
• Remains the reference standard for definitive measurements

Clinical Applications and Interpretation

• Normal range: Typically <2 mmol/L

• Monitoring frequency:

  • Initial measurement upon presentation/suspicion of shock
  • Serial measurements every 2-6 hours during resuscitation
  • More frequent measurements (hourly) may be needed in unstable patients

• Clinical significance:

  • Lactate is a sensitive marker of tissue hypoperfusion and cellular hypoxia 1
  • Elevated levels (>2 mmol/L) suggest inadequate tissue perfusion 1
  • Persistent elevation or failure to clear lactate within 24 hours associated with increased mortality 1

Important Considerations

• Sample handling:

  • Analyze samples promptly (within 15 minutes) or place on ice to prevent falsely elevated results
  • Hemolysis can falsely elevate lactate readings

• Potential pitfalls:

  • Alcohol consumption may affect reliability of lactate measurements 1
  • Tourniquet use during venous sampling can falsely elevate lactate
  • Excessive hand squeezing during capillary collection can increase lactate values

• Alternative marker:

  • Base deficit from arterial blood gas can be used as an alternative when lactate measurement is unavailable 1
  • Base deficit correlates with shock severity but is less specific for tissue hypoperfusion than lactate 1

Clinical Algorithm for Lactate Measurement

1. Initial assessment:

   • Obtain arterial or venous blood sample for lactate measurement
   • Use point-of-care testing when available for rapid results

2. Interpretation:

   • <2 mmol/L: Normal
   • 2-4 mmol/L: Mild elevation, monitor closely

   • 4 mmol/L: Significant elevation indicating tissue hypoperfusion

3. Monitoring:

   • Obtain serial measurements to track response to resuscitation
   • Target normalization of lactate levels within 24 hours 1
   • Failure to clear lactate within 24-48 hours associated with poor outcomes 1

By following these guidelines for lactate measurement, clinicians can effectively monitor tissue perfusion status and guide resuscitation efforts in critically ill patients.