What is type B lactic acidosis?

Type B Lactic Acidosis

Type B lactic acidosis is a form of metabolic acidosis characterized by elevated blood lactate levels (≥5 mmol/L) and low pH (≤7.35) that occurs in the absence of tissue hypoxia or hypoperfusion. 1 Unlike Type A lactic acidosis, which is caused by inadequate oxygen delivery to tissues, Type B occurs with normal tissue oxygenation and perfusion.

Pathophysiology

Type B lactic acidosis results from:

• Altered cellular metabolism: Occurs when cells produce excess lactate despite adequate oxygen supply
• Impaired lactate clearance: When the body cannot properly metabolize or eliminate lactate
• Mitochondrial dysfunction: Particularly relevant in drug-induced cases

Classification and Causes

Type B lactic acidosis can be subdivided into several categories:

1. Medication/Drug-Induced

• Metformin: Can cause lactic acidosis, especially in patients with renal impairment, characterized by elevated blood lactate concentrations (>5 mmol/L), anion gap acidosis, and increased lactate:pyruvate ratio 2
• Nucleoside Reverse Transcriptase Inhibitors (NRTIs): Can cause mitochondrial toxicity by inhibiting DNA polymerase γ, leading to lactic acidosis with hepatic steatosis 3

2. Malignancy-Associated

• Hematologic malignancies: Particularly lymphomas and leukemias
• Mechanism: The "Warburg effect" - cancer cells switch to glycolytic metabolism even in the presence of oxygen, producing excess lactate 4, 5
• Presentation: Can present with severe metabolic acidosis despite normal tissue perfusion 1

3. Metabolic/Enzymatic Disorders

• Thiamine deficiency (including in malignancy patients) 6
• Inherited or acquired enzymatic defects affecting lactate metabolism

4. Other Causes

• Liver disease (impaired lactate clearance)
• Diabetes mellitus
• Toxins and alcohol

Clinical Presentation

Symptoms of Type B lactic acidosis may include:

• Nonspecific gastrointestinal symptoms (nausea, vomiting, abdominal pain)
• Respiratory distress
• Generalized weakness
• Altered mental status or somnolence
• In severe cases: hypotension and bradyarrhythmias 2

Laboratory Findings

• Elevated serum lactate: Typically >5 mmol/L
• Metabolic acidosis: Low pH (<7.35), decreased serum bicarbonate
• Increased anion gap: Na − [Cl+CO2] >16 3
• Normal tissue oxygenation parameters: Distinguishing it from Type A
• Other abnormalities: May include elevated aminotransferases, creatine phosphokinase, lactic dehydrogenase, lipase, and amylase 3

Diagnostic Considerations

• Proper lactate measurement requires standardized sample handling:

  • Prechilled fluoride-oxalate tubes
  • Immediate transport on ice
  • Processing within 4 hours of collection
  • Blood collection without tourniquet or fist-clenching 3

• Lactate level interpretation:

  • 2–5 mmol/dL: Elevated (correlate with symptoms)

  • 5 mmol/dL: Abnormal

  • 10 mmol/dL: Serious and potentially life-threatening 3

Management

Management depends on the underlying cause:

1. Drug-induced cases:

   • Immediate discontinuation of the offending agent
   • For metformin-associated lactic acidosis: prompt hemodialysis to correct acidosis and remove accumulated metformin 2

2. NRTI-associated lactic acidosis:

   • Discontinuation of antiretroviral treatment
   • Intensive therapeutic strategies including bicarbonate infusions and hemodialysis
   • Consider thiamine and riboflavin supplementation 3

3. Malignancy-associated:

   • Prompt treatment of the underlying malignancy is crucial for survival 4
   • Supportive care for metabolic derangements

Prognosis

The prognosis of Type B lactic acidosis varies based on the underlying cause:

• Drug-induced: May resolve with discontinuation of the offending agent
• Malignancy-associated: Generally poor prognosis without effective treatment of the underlying malignancy 4
• Severe cases: High mortality rate, especially when diagnosis or treatment is delayed

Clinical Pitfalls

1. Delayed recognition: Type B lactic acidosis may be overlooked when clinicians focus exclusively on searching for hypoxic/hypoperfusion causes (Type A)

2. Mixed presentations: Patients may have both Type A and Type B lactic acidosis simultaneously, complicating diagnosis and management 7

3. Measurement errors: Improper handling of blood samples can lead to falsely elevated lactate levels

4. Failure to identify underlying cause: Without addressing the root cause, treatment may be ineffective

5. Malignancy-associated cases: May be the first presentation of an underlying malignancy and require thorough evaluation

Early recognition and prompt treatment of the underlying cause are essential for improving outcomes in patients with Type B lactic acidosis.