Unit Converter
Lactate (Lactic Acid)
(Key Marker of Tissue Hypoxia, Shock, Sepsis Severity & Metabolic Acidosis)
Synonyms
- Lactate
- Lactic acid
- Blood lactate
- Plasma lactate
- L-lactate (clinically measured form)
Units of Measurement
- mmol/L
- µmol/L
- mg/dL
- mg/100 mL
- mg%
- mg/L
- µg/mL
Molecular Weight
Lactic acid ≈ 90.08 g/mol
Key Unit Conversions
1 mmol/L = 90.08 mg/L
1 mg/L = 0.0111 mmol/L
1 mg/dL = 10 mg/L = 0.111 mmol/L
1 µg/mL = 1 mg/L
mg% = mg/dL
1 µmol/L = 0.001 mmol/L
Description
Lactate is the end product of anaerobic glycolysis.
It accumulates when oxygen delivery is insufficient or when metabolism shifts toward anaerobic pathways.
Produced mainly by:
- Skeletal muscle
- Red blood cells
- Brain
- Gut tissues
It is an essential biomarker in:
- Sepsis
- Shock states
- Tissue hypoxia
- Mitochondrial dysfunction
- Metabolic acidosis
Physiological Role
- Regenerated from pyruvate under low oxygen
- Recycled by liver (Cori cycle)
- Temporary energy source during intense exercise
- Modulates pH balance
Clinical Significance
HIGH Lactate (Lactic Acidosis)
(Most important clinically)
1. Shock & Tissue Hypoxia
- Septic shock
- Cardiogenic shock
- Hypovolemic shock
- Obstructive shock
- Post–cardiac arrest
2. Sepsis / Septic Shock
Surviving Sepsis Campaign:
- Lactate ≥ 2 mmol/L → sepsis-induced hypoperfusion
- Lactate ≥ 4 mmol/L → severe sepsis / high mortality risk
3. Hypoxemia / Respiratory Failure
Low oxygen → increased anaerobic glycolysis.
4. Mitochondrial Disorders
Inherited metabolic defects causing chronic high lactate.
5. Liver Failure
Impaired clearance of lactate.
6. Severe Anemia
Reduced oxygen delivery.
7. Toxins & Drugs
- Metformin (Type B lactic acidosis)
- Cyanide
- Propofol infusion syndrome
- CO poisoning
- Iron toxicity
- Isoniazid
8. Strenuous Exercise
Transient elevations, typically up to 2–4 mmol/L.
9. Diabetic Ketoacidosis
Mild to moderate elevation.
LOW Lactate
- Rarely clinically significant
- Seen in improved perfusion after resuscitation
- Nutritional ketosis states
- Lab artifact
Reference Intervals
(Tietz 8E + Mayo + Critical Care Guidelines)
Normal Fasting Lactate
- 0.5 – 2.2 mmol/L
- (45 – 198 mg/L)
Hyperlactatemia
- > 2.0 mmol/L
Severe Elevation / Lactic Acidosis
- > 4.0 mmol/L
Critical Lactate Levels
- > 5 mmol/L → high mortality risk
- > 10 mmol/L → strongly associated with severe shock / poor prognosis
Diagnostic Uses
1. Sepsis & Septic Shock
Lactate is a core marker in sepsis protocols:
- Guides fluid resuscitation
- Predicts mortality
- Monitors response to therapy
2. Shock Evaluation
Differentiates:
- Hypovolemic
- Cardiogenic
- Distributive
3. Tissue Perfusion Monitoring
Used in ICU to trend perfusion status.
4. Metabolic Acidosis Workup
Part of lactate anion gap evaluation.
5. Cardiac Arrest & Post-ROSC Prognosis
Higher lactate = worse outcomes.
6. Mitochondrial Disease Diagnosis
Persistent high lactate in children raises suspicion.
7. Toxin-Induced Metabolic Derangements
Especially metformin, cyanide, iron toxicity.
Analytical Notes
- Arterial or venous samples acceptable
- Use gray-top fluoride oxalate tube (inhibits glycolysis)
- Sample must be placed on ice and tested quickly
- Hemolysis and delayed processing falsely increase lactate
- Tourniquet use can falsely elevate results
Clinical Pearls
- Elevated lactate is a marker of mortality, not just hypoxia.
- Lactate clearance (drop in lactate after therapy) is a powerful prognostic tool.
- In sepsis: lactate ≥4 mmol/L is treated aggressively even if BP is normal.
- Mitochondrial causes → high lactate with normal oxygen delivery.
- Ketoacidosis produces moderate elevation (~3–5 mmol/L).
Interesting Fact
The body produces ~1500 mmol of lactate per day - most is recycled by the liver through the Cori cycle, converting lactate back to glucose.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Organic Acids
- Surviving Sepsis Campaign Guidelines (SSC)
- Mayo Clinic Laboratories - Lactate
- ARUP Consult - Sepsis Biomarkers
- Critical Care Society - Shock & Perfusion Monitoring
- NIH / MedlinePlus - Lactic Acid Test