Differential Diagnosis for Elevated BUN with Hyperglycemia

Single Most Likely Diagnosis

• Diabetic Ketoacidosis (DKA): This condition is characterized by hyperglycemia, metabolic acidosis, and increased levels of ketone bodies. Elevated BUN can occur due to dehydration, which is a common feature of DKA. The combination of hyperglycemia and elevated BUN makes DKA a highly plausible diagnosis.

Other Likely Diagnoses

• Dehydration: Dehydration can cause a rise in BUN due to decreased renal perfusion and concentrated blood. Hyperglycemia can also contribute to dehydration through osmotic diuresis. This diagnosis is likely, especially if the patient has been experiencing excessive thirst, dark urine, or decreased urine output.
• Sepsis: Sepsis can lead to elevated BUN due to hypoperfusion of the kidneys and can also cause hyperglycemia due to the stress response and potential insulin resistance. This diagnosis should be considered, especially if the patient has signs of infection or systemic inflammation.
• Acute Kidney Injury (AKI): AKI can result in elevated BUN due to impaired renal function. Hyperglycemia can be a contributing factor to AKI, especially if it leads to dehydration or if the patient has pre-existing kidney disease.

Do Not Miss Diagnoses

• Hyperosmolar Hyperglycemic State (HHS): Similar to DKA, HHS is a serious complication of diabetes characterized by extreme hyperglycemia and dehydration. It is crucial not to miss this diagnosis, as it has a high mortality rate if not promptly treated.
• Urosepsis: Urosepsis, or sepsis originating from a urinary tract infection, can cause both elevated BUN and hyperglycemia. Missing this diagnosis could lead to severe consequences, including septic shock and death.

Rare Diagnoses

• Pheochromocytoma: Although rare, pheochromocytoma can cause hyperglycemia due to the excess catecholamines affecting glucose metabolism. Elevated BUN could occur due to renal vasoconstriction or other indirect effects of the tumor. This diagnosis is less likely but should be considered if other signs or symptoms suggestive of pheochromocytoma are present.
• Cushing's Syndrome: Cushing's syndrome, caused by excess cortisol, can lead to hyperglycemia due to insulin resistance. Elevated BUN might be seen due to the catabolic effects of cortisol on muscle and potential renal effects. This diagnosis is rare but should be considered if there are other signs of cortisol excess.