Acute Renal Failure (ARF), now commonly referred to as Acute Kidney Injury (AKI), is a rapid decline in kidney function that leads to the accumulation of toxins and waste in the blood. This condition, though often reversible, can be life-threatening without timely diagnosis and proper treatment. This article walks you through everything you need to know about ARF—causes, signs, diagnostics, and management.
What Is Acute Renal Failure (ARF)?
Acute renal failure is a sudden loss of kidney filtration function, leading to a build-up of urea, creatinine, potassium, and fluids in the body. It can occur over hours to days and, if untreated, may progress to chronic kidney disease or death.
Anuria is defined as <100 ml/day urine output.
Oliguria is defined as <0.5 ml/kg/hr or <400 ml/day urine output.
Classification of Acute Renal Failure
ARF is typically classified based on the site of the primary pathology:
- Pre-renal: Decreased renal perfusion without parenchymal damage.
- Renal (Intrinsic): Damage to the kidney tissues.
- Post-renal: Obstruction of urine outflow.
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1. Pre-Renal Causes of Acute Renal Failure
Pre-renal failure is due to inadequate blood flow to the kidneys. It’s the most common and most reversible form of AKI.
Causes:
- Hypovolaemia (blood/fluid loss)
- Septicemia → systemic vasodilation
- Hypoxaemia
- Pancreatitis
- Liver failure
- Nephrotoxic drugs (NSAIDs, ACE inhibitors)
- Cardiogenic shock
Lab Clues:
- Urine Na⁺ < 10 mmol/L
- Urea/Creatinine ratio > 10:1
- Urine Osmolality > 500 mosm/kg
- Concentrated urine
2. Renal (Intrinsic) Causes of Acute Renal Failure
Occurs when there is structural damage to kidney tissue—glomeruli, tubules, interstitium, or vasculature.
Main Subtypes:
a. Glomerular:
- Acute glomerulonephritis
- Lupus nephritis
- Vasculitis
b. Tubular:
Acute Tubular Necrosis (ATN) from ischemia or nephrotoxins
- Causes: aminoglycosides, amphotericin B, contrast agents
c. Interstitial:
- Drugs (NSAIDs, penicillin, allopurinol)
- Infections (pyelonephritis)
d. Vascular:
- Vasculitis
- Malignant hypertension
- Thrombotic microangiopathy
Lab Features:
- Urine Na⁺ > 20 mmol/L
- Urea/Creatinine ratio ~3:1 or less
- Urine Osmolality < 400 mosm/kg
- Presence of casts, RBCs, protein
3. Post-Renal Causes of Acute Renal Failure
Result from urinary outflow obstruction. Often reversible if caught early.
Common Causes:
- Stones (calculi)
- Bladder outlet obstruction (BPH, cancer)
- Ureteric fibrosis or stricture
- Blood clots
- Primary/secondary tumors
- Worm infestations (rare)
Diagnostic Tools:
- Bladder scan
- Renal ultrasound
- Catheterization to rule out retention
Clinical Features of Acute Renal Failure
ARF typically progresses in phases:
1. Oliguric Phase (hours to weeks)
- Urine output <0.5 mL/kg/hr
- Fatigue, confusion, drowsiness
- Nausea, vomiting, diarrhoea
- Fluid overload, pulmonary edema
- Hyperkalaemia, metabolic acidosis
2. Diuretic Phase (recovery phase)
- High urine output (polyuria)
- Risk of dehydration and electrolyte loss (Na+, K+)
3. Recovery or Residual CKD Phase
- Normal renal function resumes
- May progress to Chronic Kidney Disease (CKD) in some
Investigations for Diagnosing AKI
Lab Tests:
- Urea and creatinine
- Electrolytes (especially K+)
- Arterial Blood Gas (ABG) – metabolic acidosis
- Urinalysis: protein, blood, casts
- CBC: anaemia, leukocytosis
Imaging:
- Renal Ultrasound – rule out obstruction
- CT/KUB – assess calculi or masses
- Chest X-ray – assess fluid overload
Interpretation of Key Lab Findings
| Parameter | Pre-Renal | Intrinsic | Post-Renal |
|---|---|---|---|
| Urine Na⁺ | < 10 | > 20 | Normal |
| Urea/Creatinine ratio | > 10:1 | 3:1 or less | Normal |
| Urine Osmolality | > 500 | < 400 | Normal |
| Findings | Concentrated urine | Casts, RBCs | Normal urine |
Common Causes Summarized
Pre-Renal:
- Dehydration, hemorrhage, burns, sepsis
Intrinsic:
- Glomerulonephritis, ATN, drug toxicity, myeloma
Post-Renal:
- BPH, bladder carcinoma, renal stones, neurogenic bladder
Key Management Principles
1. Prevention
- Hydration before contrast studies
- Avoid nephrotoxins (NSAIDs, aminoglycosides)
- Close monitoring in elderly, diabetics
2. Early Identification
- Catheterize to rule out retention
- Correct hypovolaemia with fluids
- Avoid large boluses in elderly
3. Ongoing Support
- Monitor fluid status
- Adjust doses of all renally-excreted drugs
- Restrict K+, phosphate, and sodium
Treatment of Established Renal Failure
- Fluid/electrolyte balance
- K⁺: insulin + dextrose, calcium gluconate, K⁺ binders
- Na⁺: restrict intake
- Diet: high calorie, low protein
- Sodium bicarbonate for acidosis
- Dialysis (haemodialysis, peritoneal, or CRRT)
Prognosis and Mortality
- In-hospital mortality: 40–50%
- ICU mortality: 70–80%
- Early intervention improves outcomes
- Delayed dialysis = poor prognosis
Essential Patient Education Points
- Stay hydrated, especially during illness
- Avoid self-medication with NSAIDs
- Control blood sugar and blood pressure
- Get regular kidney function tests if diabetic/hypertensive
- Know the signs of fluid overload and electrolyte imbalance
FAQs on Acute Renal Failure
1. Is acute renal failure reversible?
Yes, especially if pre-renal or post-renal. Intrinsic forms may take longer.
2. When is dialysis indicated?
Hyperkalaemia, volume overload, severe acidosis, or uraemic symptoms.
3. Can urine output be normal in AKI?
Yes. Not all AKI patients are oliguric.
4. How is ARF different from CKD?
ARF is acute and often reversible. CKD is progressive and usually irreversible.
5. What are the first signs of AKI?
Reduced urine output, fatigue, swelling, nausea, and confusion.
Conclusion
Acute Renal Failure or Acute Kidney Injury is a medical emergency that requires early detection, appropriate classification, and timely intervention. Whether it’s dehydration, nephrotoxicity, or obstruction, treating the underlying cause quickly is the key to recovery.
Keep the kidneys functioning—they never complain until it’s too late.
