Prerenal

Prerenal describes a pattern of kidney dysfunction caused by reduced renal perfusion before the kidney tissue itself is damaged. It is a common, often reversible, cause of acute kidney injury and is characterized by functional changes rather than intrinsic kidney parenchymal disease. If recognized and treated promptly, renal function can return to baseline.

Causes and pathophysiology include conditions that lower effective arterial blood volume or renal blood flow. These include volume depletion from dehydration, vomiting, diarrhea, or hemorrhage; conditions that reduce circulating volume such as heart failure, liver cirrhosis with ascites, or nephrotic syndrome; and systemic vasodilation from sepsis or severe allergic reactions. Medications can also contribute: nonsteroidal anti-inflammatory drugs can impair afferent arteriolar dilation, while ACE inhibitors and ARBs can reduce efferent arteriolar constriction, both decreasing renal perfusion. Inadequate fluid intake, severe burns, or renal artery stenosis may similarly create prerenal states.

Diagnosis relies on laboratory and clinical clues indicating decreased perfusion with preserved kidney structure. A typical pattern includes an elevated blood urea nitrogen to creatinine ratio (>20:1), low urine sodium (<20 mEq/L), a low fractional excretion of sodium (<1%), and concentrated urine with osmolality often >500 mOsm/kg. Hyaline casts may be seen, and the patient often shows signs of volume depletion or low effective circulating volume.

Management focuses on restoring renal perfusion and correcting the underlying cause. This may involve volume resuscitation with isotonic saline in hypovolemia, careful management of heart failure or liver disease, and avoidance or adjustment of nephrotoxic medications. If renal perfusion improves, kidney function typically recovers; failure to respond suggests progression to intrinsic kidney injury such as acute tubular necrosis.