Acute kidney injury (AKI) describes a sudden decline in kidney function, developing within hours or days. This condition replaces “acute renal failure” and encompasses a broad spectrum of kidney dysfunction. AKI is categorized into three types based on the underlying cause: prerenal, intrarenal, and postrenal. This article focuses on the characteristics of intrarenal acute kidney injury.
Understanding Intrarenal Acute Kidney Injury
Intrarenal acute kidney injury involves direct damage within kidney structures. Unlike prerenal AKI, which stems from reduced blood flow, or postrenal AKI, caused by obstructions, intrarenal AKI directly injures kidney tissue. This damage impairs the kidney’s ability to filter waste products from the blood and maintain fluid and electrolyte balance.
Key Characteristics of Intrarenal Damage
Intrarenal AKI is characterized by damage to the kidney’s internal components, including the tubules, glomeruli, and interstitium.
Acute Tubular Necrosis (ATN)
The most common form is Acute Tubular Necrosis (ATN), which damages the kidney tubules. These tubules are crucial for reabsorbing necessary nutrients and excreting waste. ATN often results from a lack of oxygen (ischemia) or exposure to substances toxic to the kidneys (nephrotoxins).
Acute Interstitial Nephritis (AIN)
Acute Interstitial Nephritis (AIN) is inflammation of the kidney’s interstitium, the tissue surrounding the tubules and glomeruli. This inflammation is often a hypersensitivity reaction to medications, such as antibiotics or nonsteroidal anti-inflammatory drugs (NSAIDs). Infections or autoimmune diseases can also trigger AIN, impairing the kidney’s filtering capabilities.
Acute Glomerulonephritis
Acute Glomerulonephritis is inflammation of the glomeruli, the tiny filtering units within the kidney. These structures filter blood and remove waste products. It often arises from immune system reactions, where the body’s immune system attacks healthy kidney tissue. Infections like strep throat or autoimmune diseases, such as lupus, can also cause this inflammation.
Vascular Damage
Vascular damage within the kidney’s small blood vessels can also lead to intrarenal AKI. Conditions like vasculitis (inflammation of blood vessels) or thrombotic microangiopathies (small blood clots in vessels) directly injure these renal blood vessels. This damage can compromise blood flow within the kidney, leading to impaired filtration and kidney dysfunction.
Common Causes of Intrarenal Kidney Injury
Various factors can lead to the direct kidney damage seen in intrarenal AKI.
Ischemia
A significant cause is ischemia, a lack of adequate blood flow and oxygen to kidney tissue. This can occur in severe dehydration, significant blood loss, or shock, where blood pressure drops dramatically. Prolonged periods of reduced blood flow can cause cellular injury and death within the kidney tubules.
Nephrotoxic Medications and Substances
Exposure to nephrotoxic medications and substances is a frequent cause of intrarenal kidney injury. Certain drugs, including antibiotics, chemotherapy agents, and contrast dyes used in medical imaging, can directly harm kidney cells. Nonsteroidal anti-inflammatory drugs (NSAIDs) and proton pump inhibitors are also known to cause kidney damage. These substances interfere with normal kidney cell function, leading to injury.
Systemic Diseases
Systemic diseases can trigger intrarenal AKI by affecting the kidneys as part of a broader condition. Autoimmune conditions like systemic lupus erythematosus can cause inflammation in the glomeruli. Severe infections, such as sepsis, can lead to widespread inflammation and reduced blood flow, damaging kidney structures. Cancers or rhabdomyolysis (muscle tissue breakdown) can release harmful substances that injure the kidneys.
Identifying Intrarenal Acute Kidney Injury
Recognizing intrarenal AKI involves evaluating clinical signs and diagnostic tests. Individuals might experience symptoms such as decreased urine output, swelling in the legs or face, fatigue, or nausea. Confusion and drowsiness can also occur, reflecting the body’s inability to clear waste products effectively and indicating the kidney’s impaired function.
Diagnostic methods begin with blood tests for creatinine and blood urea nitrogen (BUN). Elevated levels of these waste products indicate a decline in kidney filtration. Urine tests are also important, looking for abnormal components like protein or cellular casts, which can point to specific types of kidney damage. Imaging studies like ultrasound or a kidney biopsy may be performed to identify the type and extent of internal kidney damage.