Differential Diagnosis for a 71-year-old man with confusion and chest pain

Single most likely diagnosis

• Sepsis: The patient's elevated leukocyte count (15.0 × 10^3/mcL), lactate level (9 mg/dL), and confusion suggest a severe infection. The high blood pressure (220/100 mmHg) and tachycardia (120/min) also support this diagnosis. Sepsis can lead to organ dysfunction, which is indicated by the elevated creatinine (1.50 mg/dL) and BUN (45 mg/dL) levels.

Other Likely diagnoses

• Myocardial infarction: The patient's complaint of chest pain, elevated heart rate, and high blood pressure suggest a possible myocardial infarction. However, the absence of specific cardiac biomarkers (e.g., troponin) makes it less clear.
• Pulmonary embolism: Although less likely, the patient's tachycardia, confusion, and chest pain could also be indicative of a pulmonary embolism, especially in the context of possible sepsis or another underlying condition.
• Acute pancreatitis: The elevated lipase level (205 U/L) suggests pancreatitis, which could be a contributing factor to the patient's condition, possibly secondary to another primary diagnosis like sepsis.

Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

• Aortic dissection: The high blood pressure and chest pain could be indicative of an aortic dissection, which is a medical emergency requiring immediate intervention.
• Intracranial hemorrhage: The patient's confusion and high blood pressure could also suggest an intracranial hemorrhage, which would require urgent neuroimaging and possible neurosurgical intervention.

Rare diagnoses

• Pheochromocytoma: Although rare, the patient's significantly elevated blood pressure could suggest a pheochromocytoma, especially if other signs like tachycardia and sweating are present.
• Thyroid storm: The patient's tachycardia, confusion, and elevated blood pressure could also be indicative of a thyroid storm, which is a life-threatening condition requiring immediate treatment.

The laboratory finding indicative of the poorest prognosis in this patient is the lactate level. Elevated lactate levels are associated with increased mortality in critically ill patients, as they indicate tissue hypoxia and possible organ dysfunction.