Signs and Symptoms of Acute Renal Failure (ARF)/Acute Kidney Injury (AKI)
The primary signs of Acute Kidney Injury (AKI) include an increase in serum creatinine of ≥0.3 mg/dL within 48 hours, an increase in serum creatinine to ≥1.5 times baseline within 7 days, or urine output less than 0.5 mL/kg/hour for 6 hours or more. 1, 2
Laboratory and Clinical Manifestations
Diagnostic Criteria
Serum Creatinine Changes:
- Increase of ≥0.3 mg/dL within 48 hours
- Increase to ≥1.5 times baseline within 7 days
- Absolute value >4.0 mg/dL with an acute increase of at least 0.5 mg/dL 1
Urine Output Reduction:
- <0.5 mL/kg/hour for 6-12 hours (Stage 1)
- <0.5 mL/kg/hour for ≥12 hours (Stage 2)
- <0.3 mL/kg/hour for ≥24 hours or anuria for ≥12 hours (Stage 3) 3
Staging of AKI
AKI is classified into three stages according to the RIFLE criteria (Risk, Injury, Failure, Loss, End-stage kidney disease) 1:
| Stage | Serum Creatinine Criterion | Urine Output Criterion |
|---|---|---|
| 1 | 1.5-1.9 times baseline or ≥0.3 mg/dL increase | <0.5 mL/kg/h for 6-12h |
| 2 | 2.0-2.9 times baseline | <0.5 mL/kg/h for ≥12h |
| 3 | ≥3.0 times baseline or ≥4.0 mg/dL or RRT initiation | <0.3 mL/kg/h for ≥24h or anuria for ≥12h |
Clinical Signs and Symptoms
Early Signs
- Oliguria (reduced urine output) 1, 3
- Fluid retention with weight gain
- Peripheral edema
- Rising blood pressure
- Elevated BUN and creatinine 4
Advanced Signs
- Uremic symptoms:
- Nausea and vomiting
- Altered mental status
- Fatigue
- Anorexia
- Metallic taste in mouth
- Fluid overload:
- Pulmonary edema
- Dyspnea
- Pleural effusions
- Peripheral edema
- Jugular venous distention 4
- Electrolyte abnormalities:
- Hyperkalemia (elevated potassium)
- Metabolic acidosis
- Hyperphosphatemia
- Hypocalcemia 3
Urinalysis Findings
Urinalysis can help differentiate the etiology of AKI:
Prerenal AKI:
- Concentrated urine (high specific gravity)
- Low urine sodium (<20 mEq/L)
- Fractional excretion of sodium (FENa) <1%
- Fractional excretion of urea (FEUrea) <35% 3
- Benign sediment with few cellular elements
Intrinsic Renal AKI:
Postrenal AKI:
- Variable findings
- May see crystals in certain types of obstruction
- Pyuria if obstruction is complicated by infection
Special Considerations
AKI in Patients with Cirrhosis
- Standard criteria may underestimate kidney injury due to:
- Decreased creatinine production from muscle wasting
- Increased renal tubular secretion of creatinine
- Dilution of serum creatinine due to increased volume of distribution
- Interference with creatinine assays by elevated bilirubin 1
Persistent vs. Transient AKI
- Transient AKI: Complete reversal within 48 hours of onset
- Persistent AKI: Continuation of AKI beyond 48 hours 1
- Persistent AKI is associated with worse outcomes and higher mortality 1
Pitfalls in Diagnosis
Serum creatinine is an imperfect marker as it:
Urine output criteria may be misleading in:
- Patients on diuretics
- Patients with cirrhosis who may be oliguric despite normal GFR 1
Single measurements of creatinine should be interpreted with caution as levels may fluctuate spontaneously 3
Monitoring Recommendations
- Daily monitoring of serum creatinine, BUN, electrolytes, fluid balance, and hemodynamic parameters in acute settings 3
- For AKI Stage 1, monitor creatinine levels weekly 3
- For patients with hepatorenal syndrome, daily monitoring may be necessary 3
Remember that early recognition of AKI is crucial for preventing progression to more severe stages and improving outcomes. Mortality increases with higher stages of AKI, ranging from 28% to 90% depending on the severity and patient population 1.