From the Guidelines
A normal anion gap on a Comprehensive Metabolic Panel (CMP) is typically considered to be less than 28 mmol/L, as suggested by recent evidence 1. When interpreting the anion gap, it's essential to consider the formula used for calculation, which is Anion Gap = Na+ + K– Cl– HCO−, incorporating both sodium and potassium levels.
- The anion gap is a critical component of the CMP, helping clinicians diagnose and manage various conditions, including metabolic acidosis and electrolyte imbalances.
- An elevated anion gap, particularly above 28 mmol/L, has been associated with higher mortality rates, as seen in cases of ethylene glycol poisoning 1.
- It's crucial to note that laboratory reference ranges may vary, but the threshold of 28 mmol/L is supported by recent studies, such as the one published in Critical Care 1.
- Conditions like diabetic ketoacidosis, lactic acidosis, and certain poisonings can cause an elevated anion gap, while a low anion gap may be seen in hypoalbuminemia, multiple myeloma, or lithium toxicity.
- Clinicians should consider the anion gap in conjunction with other laboratory results and clinical findings to provide accurate diagnoses and effective treatment plans.
From the Research
Normal Anion Gap on a Comprehensive Metabolic Panel (CMP)
- A normal anion gap is typically considered to be between 3-12 mEq/L 2.
- The anion gap is calculated by subtracting the sum of chloride and bicarbonate ions from the sodium ion concentration in the blood.
- Anion gap metabolic acidosis occurs when the anion gap is elevated, indicating an accumulation of unmeasured anions in the blood 3, 4.
- High anion gap metabolic acidosis can be caused by various conditions, including diabetic ketoacidosis, lactic acidosis, and kidney disease 5, 4, 6.
- The diagnosis of metabolic acidosis and the calculation of the anion gap are important in determining the underlying cause of the condition and guiding treatment 2.