Which laboratory finding confirms that a child with type 1 diabetes is experiencing diabetic ketoacidosis?

A. Elevated serum carbon dioxide is incorrect because in diabetic ketoacidosis (DKA), serum bicarbonate (CO2 content) is usually decreased, reflecting metabolic acidosis rather than an elevation. B. No urinary ketones is incorrect because the presence, not absence, of ketones is characteristic of DKA. Children in DKA typically have ketonuria and ketonemia, which contribute to acidosis. C. Elevated serum phosphorus is incorrect because phosphorus levels in DKA are often normal or low due to urinary losses and shifts associated with acidosis and insulin therapy. It is not a diagnostic marker for DKA. D. Low arterial pH is correct because DKA is characterized by metabolic acidosis, reflected by a low arterial pH (<7.35). The accumulation of ketone bodies (acetoacetate and beta-hydroxybutyrate) lowers blood pH, confirming the presence of DKA.