Acute Renal Failure: Signs, Classification, and Diagnosis

Acute Renal Failure (ARF)

Signs

ARF is often asymptomatic. However, some common signs include:

• Oliguria: Urine output of less than 400 ml per day
• Increased nitrogen products in the blood
• Electrolyte and acid-base abnormalities

Classification of Acute Renal Failure

1. Pre-renal ARF

This type accounts for 55% of cases. It is characterized by a deficiency in kidney perfusion, which decreases the glomerular filtration rate (GFR). There is no frank damage to the renal parenchyma initially.

Features of Pre-renal ARF:

• Often reversible
• No initial damage to the renal parenchyma
• Prolonged deficiency can lead to ischemia and acute tubular necrosis
• The renal tubules and loop of Henle are most affected by ischemia

Phases of Pre-renal ARF:

• Extension phase: Swelling occurs, promoting ischemia
• Maintenance phase: Occurs 1-2 weeks after the initial stage, characterized by a GFR of 5-10 ml/min (low)
• Regeneration phase: Epithelial cells of the renal tubules regenerate, and the GFR gradually recovers

Clinical Picture of Pre-renal ARF:

Hypovolemia manifests as:

• Dry mucous membranes
• Dizziness
• Headache
• Thirst (due to dehydration)
• Hypotension
• Tachycardia

2. Intrinsic Renal ARF

This type accounts for 40% of cases. It involves diseases that damage the renal parenchyma.

Causes of Intrinsic Renal ARF:

• Medications, such as Ketorolac (if used for more than 10 days)
• Antibiotics, such as aminoglycosides (e.g., Amikacin), which can cause nephrotoxicity by damaging epithelial cells of the renal tubules

Clinical Picture of Intrinsic Renal ARF:

• Often asymptomatic
• General malaise
• Asthenia and weakness
• Hematuria (blood in urine)
• May cause pain

3. Post-renal ARF

This type accounts for 5% of cases. It is caused by urinary obstruction due to factors such as:

• Blood clots
• Kidney stones
• Inflammatory processes

Clinical Picture of Post-renal ARF:

• Often asymptomatic
• Pain radiating to the genitals

Diagnosis

1. Clinical Picture and Laboratory Tests

• Elevated urea and creatinine (normal creatinine is 1 mg/dl)
• Elevated potassium, phosphate, and nitrogen products
• Low sodium
• Urinalysis: Presence of proteins, granular cell casts, hemoglobin, and erythrocytes
• Creatinine clearance

2. Imaging Studies

• Ultrasound
• Magnetic resonance imaging (MRI)
• Retrograde pyelography
• Excretory urography