Option D - Serum osmolarity is the right answer.
Serum osmolarity is the most important laboratory test for confirming this disorder in this client.
The osmolarity in patient with hyperosmolar hyperglycemic nonketotic syndrome (HHNS) is usually above 320 mOsm/L. HHNS is often diagnosed by severe hyperglycemia and plasma hyperosmolarity. Potassium level, sodium level and ABG values are not as important as serum osmolarity in diagnosing HHNS.
Serum osmolarity -serum osmolarity is the most important test for confirming hhns; its also used to guide treatment strategies and determine evaluation criteria. a client with hhns typically has a serum osmolarity of more than 350 mosm/l. serum potassium, serum sodium, and abg values are also measured, but they arent as important as serum osmolarity for confirming a diagnosis of hhns. a client with hhns typically has hypernatremia and osmotic diuresis. abg values reveal acidosis, and the potassium level is variable.