Is pre-renal Acute Kidney Injury (AKI) a phase of renal Acute Kidney Injury (AKI)?

From the Guidelines

Pre-renal acute kidney injury (AKI) is a distinct category of AKI, not a phase of renal AKI. Acute kidney injury is typically classified into three main categories based on the location of the primary problem: pre-renal, intrinsic renal, and post-renal AKI [ 1 ]. Pre-renal AKI occurs when there is decreased blood flow to the kidneys, resulting in reduced kidney function despite structurally normal kidneys. This is often caused by conditions like dehydration, blood loss, heart failure, or sepsis that reduce renal perfusion [ 2 ].

Key Differences Between Pre-Renal and Renal AKI

• Pre-renal AKI is caused by decreased blood flow to the kidneys, while intrinsic or renal AKI involves direct damage to the kidney tissues themselves.
• Pre-renal AKI typically responds well to restoration of adequate renal blood flow, while intrinsic renal AKI may require more specific interventions depending on the underlying cause [ 2 ].
• The KDIGO classification system prefers to categorize AKI by cause and stage, rather than stage alone, highlighting the importance of identifying the underlying cause of AKI [ 1 ].

Importance of Accurate Diagnosis and Treatment

• Accurate diagnosis and treatment of AKI are crucial to prevent progression to chronic kidney disease (CKD) and to reduce morbidity and mortality [ 2 ].
• Evaluation of the patient with AKI includes a thorough history, physical examination, and laboratory analysis of blood and urine [ 2 ].
• Identification of the specific cause of AKI is critical, as there are different treatments for diseases such as glomerulonephritis, vasculitis, and ureteral obstruction [ 2 ].

From the Research

Definition and Classification of Pre-Renal AKI

• Pre-renal AKI is a type of acute kidney injury that occurs due to decreased renal perfusion, often caused by low intravascular volume or decreased arterial pressure 3.
• The traditional classification of acute kidney injury distinguishes between pre-renal and renal (or intrinsic) AKI, but this distinction is considered somewhat artificial by some researchers 4.

Relationship Between Pre-Renal and Renal AKI

• Pre-renal AKI is often seen as a functional and reversible condition, whereas renal AKI is associated with structural damage to the kidneys 5.
• However, the boundaries between pre-renal and renal AKI can be blurry, and some studies suggest that AKI is a continuum of injury that cannot be neatly divided into these categories 5.
• Research supports the notion that pre-renal and intrinsic AKI are distinct molecular entities, with pre-renal AKI inducing protective molecular mechanisms and intrinsic AKI requiring a 'second hit' to cause persistent damage 6.

Diagnosis and Distinction of Pre-Renal AKI

• The diagnosis of pre-renal AKI is often based on clinical evaluation, anamnestic criteria, and biochemical parameters such as the fractional excretion of sodium and the urinary-to-plasma creatinine ratio 7.
• However, these parameters can be limited by confounding factors, and the use of novel biomarkers such as NGAL and KIM-1 may provide more accurate diagnosis and distinction between pre-renal and intrinsic AKI 7.
• Urinalysis is not a reliable method for distinguishing between pre-renal and intrinsic AKI, as urinary indices can be influenced by various factors and may not accurately reflect the underlying pathology 5.