What is a normal lactic acid level?

Normal Lactic Acid Levels and Clinical Significance

Normal blood lactic acid levels are ≤2 mmol/L in most clinical settings, with values >2 mmol/L considered elevated and potentially indicative of tissue hypoperfusion or other pathological processes. 1, 2

Normal Range and Interpretation

• Normal range: ≤2 mmol/L 1, 2
• Mildly elevated: 2-5 mmol/L (requires correlation with clinical symptoms) 1, 2
• Abnormal: >5 mmol/L 1, 2
• Severe/life-threatening: >10 mmol/L 1

In some literature, normal levels have been reported as <25 mg/dL (approximately 2.8 mmol/L) in 95% of healthy individuals, with no significant differences based on age or sex 3.

Clinical Significance of Elevated Lactate

Elevated lactate levels serve as an important marker for several clinical conditions:

1. Tissue Hypoperfusion and Shock

• Serum lactate is a sensitive indicator of tissue hypoperfusion and shock 1
• Lactate is produced by anaerobic glycolysis during oxygen debt and tissue hypoperfusion 1
• Serial lactate measurements provide valuable prognostic information in circulatory shock 1

2. Mortality Prediction

• All patients with lactate levels returning to normal range (≤2 mmol/L) within 24 hours of resuscitation have been shown to survive 1
• Survival decreases to 77.8% if normalization occurs within 48 hours 1
• Survival drops to only 13.6% if lactate levels remain elevated >2 mmol/L for more than 48 hours 1

3. Sepsis Monitoring

• Lactate clearance (decrease by at least 10-20%) can be used as a resuscitation target in sepsis 1
• Lactate normalization strategies have been associated with reduced mortality in septic patients 1

Special Considerations

Pregnancy and Obstetric Patients

• In obstetric patients, lactate >2 mmol/L in the absence of labor is considered an indicator of end-organ injury 1
• During labor and immediately postpartum, lactic acid levels may be physiologically elevated and should not be used for diagnosis, though they remain important for treatment monitoring 1

Liver Disease

• Patients with liver disease may have impaired lactate metabolism 2, 4
• In critically ill patients with liver disease, lactate >2.2 mmol/L is significantly associated with increased hospital mortality 4
• Hyperlactatemia in liver disease patients is strongly associated with clinical evidence of shock 4

Alcohol Consumption

• Alcohol can increase lactate levels, potentially confounding interpretation in trauma patients 1
• However, significant elevations of blood lactate are uncommon in acute ethanol intoxication alone 5
• When lactic acidosis is found in patients with ethanol intoxication, other causes should be considered 5

Measurement Considerations

Proper sample handling is critical for accurate lactate measurement:

• Collect blood in prechilled fluoride-oxalate tubes 1
• Transport immediately on ice to the laboratory 1
• Process within 4 hours after collection 1
• Collect without using a tourniquet, without fist-clenching, and if possible, without stasis 1

Clinical Pitfalls to Avoid

1. Not considering non-hypoxic causes of lactate elevation: While tissue hypoperfusion is a common cause, lactate can be elevated due to medications, liver dysfunction, and other metabolic derangements 6

2. Misinterpreting lactate in special populations:

   • During labor and immediately postpartum 1
   • In patients with liver disease 2, 4
   • In patients with alcohol consumption 1, 5

3. Poor sample handling: Technical problems with collection and processing can lead to falsely elevated results 1

4. Focusing only on single measurements: Serial measurements provide more valuable information about prognosis and response to treatment than isolated values 1, 2