Does lipemia (elevated lipid levels in the blood) affect the anion gap on a venous blood gas (VBG)?

Impact of Lipemia on Anion Gap Measurements in Venous Blood Gas

Yes, lipemia can significantly affect anion gap measurements on venous blood gas by causing falsely low bicarbonate readings, resulting in a pseudo-anion gap metabolic acidosis. 1

Mechanism of Interference

• Pseudo-hypobicarbonatemia: Severe hypertriglyceridemia can interfere with commonly used enzymatic assays for serum bicarbonate measurement, causing falsely low or even unmeasurable serum bicarbonate levels 1
• The calculated bicarbonate derived from blood gas analyzers is not affected by lipemia 1
• This discrepancy creates an artificially elevated anion gap that does not reflect true acid-base status

Clinical Implications

• Can lead to misdiagnosis of severe anion gap metabolic acidosis
• May trigger unnecessary and expensive metabolic workups 1
• Important to recognize in patients with conditions predisposing to hypertriglyceridemia:
  • Uncontrolled diabetes
  • Alcoholism
  • Certain medications
  • Genetic disorders of lipid metabolism

Recognition and Management

• Key indicator: Visibly lipemic (milky) serum in the setting of an otherwise unexplained anion gap metabolic acidosis 1

• Recommended approach:

  1. Obtain a blood gas sample for true determination of acid-base status
  2. Compare the bicarbonate value from the blood gas analyzer with the laboratory-measured bicarbonate
  3. If discrepancy exists, consider lipemia as the cause of the falsely elevated anion gap

• In severe cases where accurate measurements are critical, therapeutic plasma exchange can correct the hypertriglyceridemia and resolve the pseudo-hypobicarbonatemia 1

Anion Gap Considerations

• Normal anion gap reference ranges have been lowered from 8-16 mmol/L to 3-11 mmol/L due to changes in electrolyte measurement techniques 2
• When monitoring acid-base status in patients with suspected lipemia, venous pH and direct blood gas measurements are more reliable than calculated anion gap 3
• During treatment of conditions like DKA, venous pH (typically 0.03 units lower than arterial pH) and anion gap can be followed to monitor resolution of acidosis 3

Prevention of Misdiagnosis

• Always inspect serum samples for lipemia when encountering unexplained anion gap elevation
• Consider alternative methods for bicarbonate measurement when lipemia is present
• Document the presence of lipemia in laboratory reports to alert clinicians to potential interference

By recognizing this laboratory artifact, clinicians can avoid unnecessary diagnostic workups and interventions while focusing on appropriate management of the underlying condition causing hypertriglyceridemia.