From the Guidelines
Yes, a patient can have non-anion gap metabolic acidosis, as evidenced by the development of transient non–anion gap metabolic acidosis in patients recovering from diabetic ketoacidosis (DKA) due to the use of excessive saline for fluid and electrolyte replacement, as noted in a study published in Diabetes Care 1. This condition is characterized by a normal anion gap despite the presence of metabolic acidosis, and it can occur when bicarbonate is lost from the body or when chloride is retained in excess.
- Common causes of non-anion gap metabolic acidosis include:
- Diarrhea, leading to direct bicarbonate loss from the gastrointestinal tract
- Renal tubular acidosis (RTA), where the kidneys fail to properly reabsorb bicarbonate or excrete acid
- Use of carbonic anhydrase inhibitors like acetazolamide
- Administration of chloride-containing solutions such as normal saline, especially in large volumes, as seen in patients recovering from DKA 1
- The hallmark laboratory findings of non-anion gap metabolic acidosis include:
- Low serum bicarbonate level
- Low pH
- Normal anion gap
- Elevated serum chloride levels (hyperchloremia) that balance the decrease in bicarbonate Treatment of non-anion gap metabolic acidosis depends on addressing the underlying cause, such as stopping the offending medication, treating diarrhea, or providing bicarbonate supplementation in cases of RTA, and understanding the distinction between anion gap and non-anion gap metabolic acidosis is crucial for proper diagnosis and management of acid-base disorders, as highlighted in the context of DKA recovery 1.
From the Research
Non-Anion Gap Metabolic Acidosis
- Non-anion gap metabolic acidosis can present as a form of either acute or chronic metabolic acidosis, as seen in a case of high-volume ileostomy output causing large bicarbonate losses 2.
- This condition can result from kidney or nonkidney disorders, and a complete clinical history and physical examination are critical initial steps to begin the evaluation process 2, 3.
- The differential diagnosis of non-anion gap metabolic acidosis involves evaluating renal acidification, electrolyte patterns, and serum potassium concentration to characterize the disorder as hyperkalemic or hypokalemic in nature 3.
Causes and Diagnosis
- Non-anion gap metabolic acidosis can be caused by disorders of renal tubular H + transport, decreased renal ammonia secretion, gastrointestinal and kidney losses of bicarbonate, dilution of serum bicarbonate from excessive intravenous fluid administration, or addition of hydrochloric acid 4.
- The diagnosis of non-anion gap metabolic acidosis involves measuring serum electrolytes, blood gas, urine pH, and either direct or indirect urine ammonium concentration 2, 3.
- A systematic approach to the differential diagnosis of non-anion gap metabolic acidosis is essential to establish the underlying cause of the acidosis 3, 4.
Treatment
- The treatment of acute non-anion gap metabolic acidosis often involves administration of base, but the blood pH and/or serum bicarbonate concentration to guide the initiation of treatment has not been established for this type of metabolic acidosis 5.
- Therapeutic complications resulting from base administration, such as volume overload, exacerbation of hypertension, and reduction in ionized calcium, are likely to be as common as with high anion gap metabolic acidosis 5.