Final answer:
The priority assessment for a patient with symptoms suggestive of diabetes mellitus is to obtain the blood sugar level, which will confirm hyperglycemia and inform subsequent treatment interventions.
Step-by-step explanation:
The assessment that would be a priority for the nurse to obtain first for a 77-year-old female with a 2-week history of polyuria, fatigue, and ketotic breath is the c. blood sugar level. These symptoms are suggestive of diabetes mellitus, and checking the blood sugar level can confirm hyperglycemia, a hallmark of the condition. Elevated blood sugar can lead to polyuria (frequent urination) as the kidneys attempt to excrete excess glucose, and the presence of ketotic breath indicates that the body might be resorting to fat metabolism for energy, producing ketones, due to lack of glucose utilization which characterizes diabetes.
Moreover, diabetes mellitus can also result in significant alterations in fluid and electrolyte balance, impacting potassium levels and other electrolytes, but confirmation of hyperglycemia is essential for a timely and appropriate treatment strategy.