Final answer:
The best option is to assess the blood glucose level as the patient has a history of Addison's disease and complains of pain in the abdomen and weakness.
Step-by-step explanation:
The best option in this case would be to assess the blood glucose level as the patient has a history of Addison's disease and complaints of pain in the abdomen as well as weakness. Addison's disease is characterized by reduced production of cortisol from the adrenal gland, which can lead to hypoglycemia. Therefore, it is important to determine the blood glucose level to assess if this is the cause of the patient's symptoms.