Dehydration: This is the most common cause of an elevated BUN, especially to this degree. Dehydration leads to a decrease in blood volume, which in turn reduces blood flow to the kidneys, causing an increase in BUN levels as the kidneys concentrate the urine to conserve water.

Acute Kidney Injury (AKI): Conditions such as ischemia, toxins, or obstruction can cause AKI, leading to a significant elevation in BUN levels as the kidneys fail to adequately filter waste products from the blood.
Chronic Kidney Disease (CKD): Advanced stages of CKD can result in elevated BUN levels due to the progressive loss of kidney function.
Heart Failure: Reduced cardiac output can lead to decreased renal perfusion, resulting in elevated BUN levels.
Gastrointestinal Bleeding: Significant blood loss into the gastrointestinal tract can be reabsorbed, increasing the amount of urea in the blood, thus elevating BUN levels.

Sepsis: Although not as directly linked to elevated BUN as other conditions, sepsis can cause AKI and dehydration, both of which can significantly elevate BUN levels. Missing sepsis can be fatal.
Obstructive Uropathy: Blockage of the urinary tract can cause a rapid increase in BUN levels. This condition requires prompt intervention to prevent permanent kidney damage.
Rhabdomyolysis: Muscle breakdown can release large amounts of myoglobin into the blood, which can cause AKI. Early recognition is crucial for effective management.

Leukemia or Lymphoma: Certain types of cancer can infiltrate the kidneys or cause hyperuricemia, leading to elevated BUN levels.
Multiple Myeloma: This plasma cell disorder can cause kidney damage through various mechanisms, including hypercalcemia, light chain deposition, and hyperuricemia, leading to elevated BUN levels.
Hemolytic-Uremic Syndrome (HUS) and Thrombotic Thrombocytopenic Purpura (TTP): These are rare disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and AKI, which can result in elevated BUN levels.