Serum sodium concentration
Serum chloride concentration
Serum bicarbonate concentration
Clinical Interpretation
- Normal (6-12 mEq/L): Normal acid-base balance
- Elevated (>12 mEq/L): Metabolic acidosis with unmeasured anions
- Low (<6 mEq/L): May indicate hypoalbuminemia, multiple myeloma, or other conditions
Anion Gap Calculator
The anion gap is a calculated value that helps assess acid-base balance and identify the presence of unmeasured anions in metabolic acidosis. It represents the difference between measured cations and measured anions in the serum.
Formula
The anion gap is calculated using the following formula:
Normal Range
The normal anion gap is typically 6-12 mEq/L, though this may vary slightly between laboratories.
Clinical Interpretation
Normal Anion Gap (6-12 mEq/L)
- Normal acid-base balance
- May be seen in hyperchloremic metabolic acidosis
- Common causes: diarrhea, renal tubular acidosis, early renal failure
Elevated Anion Gap (>12 mEq/L)
Indicates the presence of unmeasured anions, typically seen in metabolic acidosis. Common causes include:
- Lactic acidosis: Sepsis, shock, tissue hypoxia, medications (metformin)
- Ketoacidosis: Diabetic ketoacidosis, alcoholic ketoacidosis, starvation
- Toxic ingestions: Methanol, ethylene glycol, salicylates
- Renal failure: Uremic acidosis
- Rhabdomyolysis: Muscle breakdown products
Low Anion Gap (<6 mEq/L)
Less common but may indicate:
- Hypoalbuminemia: Albumin is a major unmeasured anion
- Multiple myeloma: Monoclonal proteins
- Lithium toxicity: Lithium acts as a cation
- Bromide intoxication: Bromide measured as chloride
- Hypercalcemia: Calcium acts as a cation
Clinical Applications
- Metabolic acidosis evaluation: Helps determine the underlying cause
- Toxicology: Elevated anion gap may indicate toxic ingestions
- Critical care: Monitoring acid-base status in critically ill patients
- Renal function assessment: Helps evaluate renal tubular function
Important Considerations
- The anion gap should be interpreted in the context of the complete clinical picture
- Normal ranges may vary between laboratories
- Albumin levels affect the anion gap (hypoalbuminemia may mask an elevated gap)
- Consider the delta-delta ratio when evaluating mixed acid-base disorders
- Always correlate with other laboratory values and clinical findings
Delta-Delta Ratio
When evaluating mixed acid-base disorders, the delta-delta ratio can be helpful:
- 1.0-2.0: Simple anion gap metabolic acidosis
- >2.0: Anion gap acidosis + metabolic alkalosis
- <1.0: Anion gap acidosis + non-anion gap acidosis
This calculator provides a quick and accurate way to determine the anion gap, aiding in the evaluation of acid-base disorders and metabolic acidosis.
References
- Emmett, M., & Narins, R. G. (1977). Clinical use of the anion gap. Medicine, 56(1), 38-54.
- Kraut, J. A., & Madias, N. E. (2007). Serum anion gap: its uses and limitations in clinical medicine. Clinical Journal of the American Society of Nephrology, 2(1), 162-174.
- Gabow, P. A., Kaehny, W. D., Fennessey, P. V., Goodman, S. I., Gross, P. A., & Schrier, R. W. (1980). Diagnostic importance of an increased serum anion gap. New England Journal of Medicine, 303(15), 854-858.
- Winter, S. D., Pearson, J. R., Gabow, P. A., Schultz, A. L., & Lepoff, R. B. (1990). The fall of the serum anion gap. Archives of Internal Medicine, 150(2), 311-313.
- Feldman, M., Soni, N., & Dickson, B. (2005). Influence of hypoalbuminemia or hyperalbuminemia on the serum anion gap. Journal of Laboratory and Clinical Medicine, 146(6), 317-320.
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