The urine anion gap: the critical clue to resolve a diagnostic dilemma in a patient with ketoacidosis

Clinical utility of anion gap in deciphering acid-base disorders

The anion gap (AG) measurement is a very useful tool in the evaluation of patients with acid-base disorders. Once metabolic acidosis is identified, AG will provide the important first step in the differential diagnosis of disorders that either increase the AG and those that leave the AG unchanged. Delta gap is the comparison between change (delta) in the AG and the change (delta) in bicarbonate (HCO(3)(-)). Delta ratio, defined as delta AG:delta HCO(3)(-) is usually 1:1 in patients with an uncomplicated high AG acidosis. A value below 1:1 suggests a combined high and normal AG acidosis. A value above 2:1 suggests a combined metabolic alkalosis and a high AG acidosis. Urine AG (unmeasured anions-unmeasured cations) is an indirect estimate of the urine NH(4)(+) excretion. It is typically negative in patients with normal AG metabolic acidosis secondary to diarrhoea. Utilisation of AG calculations helps clinicians in identifying and treating acid-base disorders.

Severe acidosis caused by starvation and stress

A 1-year-old boy had severe anoxic brain injury owing to a cardiorespiratory arrest. He had an initial metabolic acidosis, but this largely resolved by hospital day 2. He then had a persistent, profound metabolic acidosis. Evaluation on hospital day 6 found that the patient had ketonemia, ketonuria, and a normal serum glucose level; he had received no intravenous dextrose during his hospitalization. The dextrose-free fluids were given initially to protect his brain from the deleterious effects of hyperglycemia after brain injury. Continuation beyond 24 hours was inadvertent. The initiation of dextrose-containing intravenous fluids produced a rapid resolution of his metabolic acidosis. Starvation usually produces a mild metabolic acidosis, but when combined with physiologic stress, starvation may cause a severe metabolic acidosis. Among the few reports of severe starvation ketoacidosis, our case is unique because the patient was monitored closely in an intensive care unit, allowing us to describe the time course of the acidosis in detail.

The syndrome of alcoholic ketoacidosis

PURPOSE

To further elucidate the clinical spectrum of alcoholic ketoacidosis (AKA).

PATIENTS AND METHODS

A case series of 74 patients with AKA defined as a wide anion gap metabolic acidosis unexplained by any other disorder or toxin, including any patient with a history of chronic alcohol abuse. The setting was the Medical Emergency Department at Grady Memorial Hospital in Atlanta, Georgia, a university-affiliated inner-city hospital.

RESULTS

AKA is a common disorder in the emergency department, more common than previously thought. The acid-base abnormalities are more diverse than just a wide-gap metabolic acidosis and often include a concomitant metabolic alkalosis, hyperchloremic acidosis, or respiratory alkalosis. Lactic acidosis is also common. Semiquantitative serum acetoacetate levels were positive in 96% of patients. Elevated blood alcohol levels were present in two thirds of patients in whom alcohol levels were determined, and levels consistent with intoxication were seen in 40% of these patients. Electrolyte disorders including hyponatremia, hypokalemia, hypophosphatemia, hyperglycemia, hypocalcemia, and hypomagnesemia were common on presentation. The most common symptoms were nausea, vomiting, and abdominal pain. The most common physical findings were tachycardia, tachypnea, and abdominal tenderness. Altered mental status, fever, hypothermia, or other abnormal findings were uncommon and reflected other underlying processes.

CONCLUSIONS

AKA is a common disorder in chronic malnourished alcoholic persons. The acid-base abnormalities reflect not only the ketoacidosis, but also associated extracellular fluid volume depletion, alcohol withdrawal, pain, sepsis, or severe liver disease. Although the pathophysiology is complex, the syndrome is rapidly reversible and has a low mortality.

The urine pH: a potentially misleading diagnostic test in patients with hyperchloremic metabolic acidosis

The purpose of this case report is to illustrate that the urine pH may be a misleading index in the assessment of the normal renal response to metabolic acidosis. On presentation, the patient had a normal anion-gap type of metabolic acidosis; the cause of the acidosis was gastrointestinal bicarbonate loss. Since the urine pH was 6.0 when the patient was acidemic, distal renal tubular acidosis was also suspected. However, since the kidneys generated more than 190 mmol of bicarbonate per day (urine ammonium was 190 mmol/d), reduced renal acid excretion was not the cause of the acidosis. Therefore, the urine pH of 6.0 provided a false clue with respect to a renal cause for the acidosis in this setting; in contrast, the urine anion gap provides more reliable information concerning bicarbonate generation by the kidney.

The urine anion gap: a clinically useful index of ammonium excretion

In patients with a normal plasma anion gap type of metabolic acidosis, knowledge of the rate of ammonium excretion can provide valuable information to determine if there is a renal cause for the disorder. Unfortunately, few hospital biochemistry laboratories offer routine determination of the urine ammonium concentration. Data are presented that demonstrate a direct linear relationship between the urine anion gap (Na+ + K+ - Cl-) and the urine ammonium concentration. In a 24-hour urine collection, the relationship is urine ammonium equals -0.8 (urine anion gap) +82 (r = 0.97 p less than 0.01). The applications of this index of ammonium excretion are discussed.