Lactate Measurement with Blood Cultures in Febrile Patients
Yes, lactate levels should be measured when ordering blood cultures for patients with fever, even with normal WBC count and viral panel, as it is a critical component of early sepsis recognition and risk stratification. 1
Rationale for Lactate Measurement
Lactate measurement provides valuable information regardless of WBC count for several reasons:
- Lactate is a direct marker of tissue hypoxia and hypoperfusion, serving as an early indicator of sepsis before other clinical signs develop 2
- The Surviving Sepsis Campaign guidelines explicitly recommend measuring lactate level within 3 hours as part of the initial sepsis bundle 1
- Even patients with normal WBC counts can have serious bacterial infections and sepsis, as WBC count has limited utility (AUC <0.70) for predicting sepsis 3
- Lactate levels correlate with mortality risk independent of organ dysfunction and shock 4
Clinical Significance of Lactate Levels
Lactate levels provide prognostic information across different ranges:
- Normal range (≤2.0 mmol/L): Even within this range, values >1.4 mmol/L are associated with increased mortality compared to values ≤1.4 mmol/L 5
- Intermediate range (2.1-3.9 mmol/L): Associated with 25% in-hospital mortality 6
- High range (≥4.0 mmol/L): Associated with 38% in-hospital mortality and sixfold higher odds of acute-phase death 6
Algorithm for Lactate Measurement in Febrile Patients
For all patients with fever and suspected infection requiring blood cultures:
If lactate is elevated (>2 mmol/L):
- Initiate appropriate antibiotics immediately
- Consider more aggressive monitoring
- For lactate ≥4 mmol/L: Administer 30 mL/kg crystalloid fluid bolus 1
If initial lactate is normal but clinical suspicion remains high:
- Proceed with antibiotics if clinically indicated
- Consider repeat lactate measurement in 2-4 hours if clinical status changes
Advantages Over Other Biomarkers
- Lactate outperforms WBC count and neutrophil count for predicting severe outcomes in sepsis 3
- While procalcitonin has better performance for diagnosing bloodstream infection (AUROC 0.83), lactate provides critical information about tissue perfusion 7
- The combination of lactate with other clinical parameters improves risk stratification 2
Important Considerations
- Lactate-guided resuscitation is associated with significant mortality reduction (RR: 0.67) compared to resuscitation without lactate monitoring 2
- Lactate normalization within 24 hours is associated with 100% survival in septic patients 2
- Even patients with viral infections can develop tissue hypoperfusion and elevated lactate levels
- Medications like epinephrine can cause lactate elevation independent of tissue perfusion 2
Measuring lactate when ordering blood cultures is a simple, cost-effective way to risk-stratify patients and identify those who may need more aggressive management, regardless of WBC count or suspected viral etiology.