Differential Diagnosis

Although the exact definition of DKA is variable, most experts agree that a blood glucose greater than 250 mg/dL, bicarbonate level less than 15 meq/L, and an arterial pH of less than 7.3 with moderate ketonemia constitute the disease.2

The differential diagnosis of metabolic coma in a diabetic patient includes hypoglycemia, nonketotic hyperosmotic coma, alcoholic ketoacidosis, lactic acidosis, and other causes of wide anion gap acidosis. A rapid differentiation can be made in the emergency department using glucose reagent strips, urine dipsticks for ketones, and blood gas analysis. As an initial rapid diagnostic step, the finding of elevated glucose with the concomitant detection of ketones by near-patient testing methods, and the presence of metabolic acidosis on venous or arterial blood gas analysis, has few rival diagnoses other than DKA. However, evaluation of the anion gap is usually superior to pH or [HCO3-] determination alone, because any "widening" of the anion gap is independent of potentially masking effects of concurrent other acid/base disturbances. The clinician who is not well acquainted with the nuances of blood gas interpretation ( Chap 21), will be confused when the pH and [HCO3-]

are not much altered from normal. Although the pH and [HCO3-] are usually examined to determine the presence of an acidosis, both can be affected by concurrent acid/base disturbances as may occur when metabolic alkalosis is also present (pH and [HCO 3-] affected) or when respiratory alkalosis is also present (pH affected). Patients with hyperosmolar, nonketotic coma tend to be older, have a more prolonged course, and have prominent mental status changes. Their serum glucose levels are generally much higher (>1000 mg/dL), and they have little to no anion gap metabolic acidosis.

The differential diagnosis of DKA includes any entity that causes a high anion gap metabolic acidosis. These include alcoholic or starvation ketoacidosis, uremia, lactic acidosis, and various ingestions (e.g., methanol, ethylene glycol, and aspirin). The ketosis in alcoholic ketoacidosis and starvation ketosis tends to be milder and glucose is usually low or normal. bHB predominates in alcoholic ketoacidosis so the urinary ketone test may be negative. If an ingestion is suspected, serum osmolarity or drug-level testing is required. Depending on the hemodynamic status, lactic acidosis (poor perfusion) may occur simultaneously with DKA; in these cases, serum lactate levels are indicated. The absence of, or presence of, only moderate ketonemia should elicit a search for lactic acidosis, as its presence favors the undetected bHOB as the predominant ketone.

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