Lactic Acid is NOT Measured in a Complete Blood Count (CBC)
Lactic acid (lactate) is a separate blood test that requires its own blood sample and is not included in a standard CBC panel. A CBC measures cellular components of blood—red blood cells, white blood cells, platelets, hemoglobin, and hematocrit—while lactate is a biochemical marker measured through different laboratory methods 1.
What a CBC Actually Measures
A Complete Blood Count includes:
- Red blood cell count, hemoglobin (Hb), and hematocrit (Hct) - these reflect oxygen-carrying capacity and can indicate blood loss, though initial values may not accurately reflect acute hemorrhage 2
- White blood cell count and differential - markers of infection or inflammation
- Platelet count - important for coagulation assessment 2
How Lactic Acid is Actually Measured
Lactate requires a separate blood sample and can be obtained from:
- Arterial blood - considered the gold standard for assessing tissue perfusion and metabolic acidosis 2, 3
- Venous blood - provides complementary information about tissue oxygen extraction 3
- Mixed venous blood - offers information about overall tissue metabolism 3
The test is typically performed on arterial blood gas (ABG) analysis or as a separate serum/plasma measurement 2.
Clinical Importance of Lactate Testing
Lactate is a sensitive marker for estimating bleeding, shock severity, and tissue hypoperfusion 2. Key clinical applications include:
- Hemorrhagic shock assessment - elevated lactate indicates tissue hypoxia from inadequate oxygen delivery 2
- Sepsis monitoring - lactate-guided resuscitation reduces mortality in septic shock 2
- Trauma evaluation - serial lactate measurements predict survival, with normalization within 24 hours associated with 100% survival 3
- Prognostic value - lactate >2.2 mM is associated with increased hospital mortality 4
Critical Preanalytical Considerations
Blood samples for lactate measurement must be handled properly to avoid falsely elevated results 5:
- Samples should be placed on crushed ice immediately if measurement is delayed
- Avoid prolonged venous stasis (>2 minutes causes elevation) 5
- At room temperature, lactate increases by 0.78 mmol/L per hour in test tubes 5
- Samples kept on ice remain stable for up to 4 hours 5
Common Clinical Pitfall
Do not confuse base deficit (measured on ABG) with lactate - while both indicate tissue hypoperfusion and shock severity, they are distinct measurements 2. Base deficit can serve as an alternative when lactate cannot be measured, though lactate more specifically reflects tissue hypoperfusion 2.