What is the primary laboratory finding that distinguishes Hyperosmolar Hyperglycemic State (HHS) from Diabetic Ketoacidosis (DKA)?

Choice A reason: Decreased blood pH is a hallmark of DKA due to metabolic acidosis from ketone accumulation. In HHS, pH is usually normal or only mildly decreased because ketosis is minimal or absent. Choice B reason: Severe hyperglycemia is present in both HHS and DKA, though it tends to be more extreme in HHS. However, it is not the distinguishing feature, as both conditions involve elevated glucose levels. Choice C reason: Ketone presence in the urine is a key feature of DKA, resulting from fat breakdown due to insulin deficiency. In HHS, ketones are typically absent or minimal, but this absence alone does not distinguish the condition as clearly as osmolality. Choice D reason: Elevated serum osmolality is the defining laboratory feature of HHS. It reflects profound dehydration and hyperglycemia without significant ketosis. This finding helps differentiate HHS from DKA and guides fluid and electrolyte management.