What is the most common cause of acute kidney injury in hospitalized patients?

• A. Postrenal obstruction.
• B. Intrinsic renal disease.
• C. Prerenal causes due to volume depletion or decreased perfusion.
• D. Chronic kidney disease.

Answer: (C)

The main idea here is that reduced blood flow to the kidneys is the most common cause of acute kidney injury in hospitalized patients. In the hospital, people often become volume depleted from vomiting, diarrhea, poor intake, or diuretic use, and they may also have conditions that lower effective circulating volume, like heart failure, sepsis, or liver disease. When the kidneys don’t receive enough blood, their filtration rate drops quickly. The body preserves water and sodium, so urine is relatively concentrated and BUN tends to rise more than creatinine, reflecting prerenal physiology. If perfusion is restored promptly with fluids and by treating the underlying illness, kidney function commonly recovers. If this reduced perfusion continues, it can progress to intrinsic kidney injury, such as acute tubular necrosis, but the initial and most frequent trigger in hospitalized patients is prerenal, rather than obstruction or chronic kidney disease. Postrenal causes and intrinsic renal diseases do occur but are less common as the first event in this setting.