Differential Diagnosis for Hyperkalemia, High BUN, and Normal Creatinine after Surgery

Single Most Likely Diagnosis

• Hemolysis or Rhabdomyolysis: This condition can lead to hyperkalemia due to the release of potassium from damaged red blood cells or muscle cells. A high BUN can occur due to the release of nitrogenous waste products from the breakdown of cells, while creatinine levels might remain normal if the renal function is not severely impaired.

Other Likely Diagnoses

• Dehydration: Dehydration can cause a pre-renal state leading to a high BUN due to concentrated urine and decreased renal perfusion. Hyperkalemia can occur if the dehydration is severe enough to impair renal function, even if creatinine levels remain within the normal range.
• Bleeding or Hemorrhage: Internal bleeding can lead to a high BUN due to the breakdown of blood cells and the release of nitrogenous waste. Hyperkalemia can result from the release of potassium from lysed red blood cells.
• Medication Side Effects: Certain medications, such as ACE inhibitors, ARBs, or potassium-sparing diuretics, can cause hyperkalemia. If these medications are continued post-surgery, they could contribute to elevated potassium levels.

Do Not Miss Diagnoses

• Acute Kidney Injury (AKI): Although creatinine levels are normal, AKI can still occur, especially if the injury is in its early stages or if the patient has a significant amount of muscle mass loss. AKI can lead to hyperkalemia and elevated BUN.
• Adrenal Insufficiency: This condition can cause hyperkalemia due to the lack of aldosterone, which regulates potassium excretion. Adrenal insufficiency can be life-threatening if not recognized and treated promptly.
• Type 4 Renal Tubular Acidosis (RTA): This condition is characterized by hyperkalemia and a high BUN due to impaired renal acidification and potassium excretion.

Rare Diagnoses

• Pseudohyperkalemia: This is a condition where the elevated potassium levels are not due to a true increase in serum potassium but rather an artifact of the blood collection or laboratory analysis process.
• Familial Hyperkalemic Periodic Paralysis: A rare genetic disorder that affects potassium channels, leading to episodes of hyperkalemia and muscle weakness.
• Liddle Syndrome: A rare genetic disorder characterized by excessive sodium absorption and potassium wasting in the kidneys, although it typically presents with hypokalemia, there might be rare instances where it could contribute to hyperkalemia in specific contexts.