From the Guidelines
The anion gap is a critical diagnostic tool in clinical medicine, helping identify the cause of metabolic acidosis, with a normal range typically between 8-12 mEq/L, and an elevated anion gap suggesting the presence of unmeasured acids in the bloodstream.
Significance of Anion Gap
The anion gap calculation is essential in distinguishing between different types of metabolic acidosis, guiding further testing, and monitoring treatment effectiveness 1.
- An elevated anion gap points to conditions like diabetic ketoacidosis, lactic acidosis, certain poisonings (methanol, ethylene glycol, salicylates), or kidney failure.
- A normal anion gap metabolic acidosis indicates conditions such as diarrhea, renal tubular acidosis, or early kidney injury.
Clinical Implications
Understanding the anion gap allows for more targeted and effective patient management in emergency and critical care settings, as high anion gap acidosis typically results from the addition of acids to the body, while normal anion gap acidosis usually stems from bicarbonate loss or failure to excrete acid 1.
Threshold for Intervention
An anion gap greater than 27 mmol/L is a recommended threshold for initiating extracorporeal treatment (ECTR) in patients with ethylene glycol poisoning 1.
- This threshold is crucial in determining the need for ECTR, as mortality rates are significantly higher in patients with an anion gap above 28 mmol/L 1.
Conclusion is not allowed, so the answer will be ended here.
From the Research
Significance of the Anion Gap
The anion gap is a mathematical construct that compares the blood sodium concentration with the sum of the chloride and bicarbonate concentrations 2, 3. It is a helpful calculation that divides the metabolic acidoses into two categories: high anion gap metabolic acidosis (HAGMA) and hyperchloremic metabolic acidosis, thereby delimiting the potential etiologies of the disorder.
Clinical Utility
- The anion gap is significant in identifying the presence of acidosis, with significant elevations almost always signifying the presence of an acidosis that can be easily identified 2.
- Anion gap acidoses can be divided into those caused by lactate accumulation, ketoacid production, toxin/drugs, and uremia 2.
- The anion gap can provide vital clues that direct the clinician toward the correct diagnosis, and its calculation can be corrected for hypoalbuminemia and severe hyperglycemia 3.
- Plasma osmolality and osmolal gap calculations can be used together with the anion gap to guide appropriate clinical decision making 3.
Limitations
- A decrease in anion gap has little clinical utility due to numerous mechanisms causing it 2.
- The serum anion gap has limitations in evaluating acid-base disorders, including a wide range of normal values and the effect of retained anion type on the magnitude of the increase in anion gap 4.
- The anion gap may not identify mild disturbances in acid-base balance, and its effectiveness can be improved by identifying the baseline value for individuals 4.
Causes of High Anion Gap Metabolic Acidosis
- Lactic acidosis caused by decreased oxygen delivery or defective oxygen utilization 2.
- Ketoacidosis usually secondary to diabetes or alcohol 2.
- Toxin-induced anion gap acidoses, including methanol, ethylene glycol, and salicylates 2, 5.
- Uremia associated with a mild acidosis secondary to decreased ammonia secretion and an anion gap caused by the retention of unmeasured anions 2.
- Organic acids, including 5-oxoproline (pyroglutamic acid), are rare but important causes of anion gap metabolic acidosis 5.