Approach to altered mental status Quiz: Ace Your Exams

A 65-year-old man presents to the emergency department with confusion and lethargy over the past week. The patient has been increasingly fatigued and has lost a significant amount of weight over the past two months. Over the past several days, he has also experienced nausea, vomiting, increased thirst, and frequent urination. Additionally, he has had a persistent cough for the past three months. He has a 40-pack-year smoking history and has not seen a physician in several years. Temperature is 37.0 °C (98.6 °F), pulse is 90/min, respiratory rate is 18/min, blood pressure is 148/80 mmHg, and oxygen saturation is 94% on room air. On physical examination, the patient is disoriented to time, and place and has dry mucous membranes. There are no focal neurological deficits, but generalized weakness is present. Cardiovascular exam is unremarkable. Diffuse Rhonchi are heard over the left lung field. Laboratory results are shown below. Which of the following is the best next step in determining the cause of this patient’s altered mental status?

Serum Chemistry	Results	Reference Range
Sodium	140 mEq/L	136-146 mEq/L
Potassium	3.8 mEq/L	3.5-5 mEq/L
Chloride	98 mEq/L	95-105 mEq/L
Creatinine	1.2 mg/dL	0.6-1.2 mg/dL
Calcium	13.6 mg/dL	8.4-10.2 mg/dL
Glucose	100 mg/dL	70-110 mg/dL
Albumin	3.4 g/dL	3.5-5.5 g/dL
Phosphorous	2.9 mg/dL	3-4.5 mg/dL