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Acute Kidney Injury
Aka: Acute Kidney Injury, Acute Renal Failure, Acute Renal Insufficiency, Renal Failure, Azotemia, Uremia, Acute Tubular Necrosis, Acute Intrinsic Renal Failure
- See Also
- Acute Interstitial Nephritis
- Acute Prerenal Failure
- Acute Postrenal Failure
- Acute Kidney Injury Causes
- Medication Causes of Acute Kidney Injury
- Nephrotoxicity Risk
- Intravenous Contrast Related Acute Renal Failure
- Chronic Renal Failure
- Prevention of Kidney Disease Progression
- Epidemiology
- Incidence of Acute Kidney Injury
- Overall: 2-3 per 1000 persons
- Hospital: 7% of patients
- ICU: Two thirds of patients
- Definitions
- Acute Kidney Injury
- Abrupt onset (within 48 hours) and
- Reduced Renal Function (Serum Creatinine elevation) and/or
- Urine output decreased and/or
- Renal replacement therapy (Dialysis)
- Uremia
- Blood homeostasis defects related to Renal Failure
- Includes Fluid Overload, Hyperkalemia and Metabolic Acidosis
- Azotemia
- Accumulation of nitrogen waste products in the blood (Blood Urea Nitrogen)
- Causes
- See Acute Renal Failure Causes
- Prerenal Failure
- See Acute Prerenal Failure
- See Prerenal Failure Causes
- See Medication Causes of Prerenal Failure
- Shock states
- Hypovolemic shock (e.g. Hemorrhagic Shock, dehydration)
- Cardiogenic Shock (CHF)
- Septic Shock
- Anaphylactic shock
- Intrinsic Renal Failure Causes
- See Intrinsic Renal Failure Causes
- Vascular Injury (e.g. Renal Artery Stenosis)
- Glomerulonephritis (e.g. SLE, PSGN)
- Malignant Hypertension
- Interstitial
- See Acute Interstitial Nephritis
- See Medication Causes of Interstitial Nephritis
- Tubular (most common intrinsic cause)
- See Acute Tubular Necrosis (20-30% of Acute Kidney Injury Causes)
- See Medication Causes of Acute Tubular Necrosis
- Postrenal Failure
- See Acute Postrenal Failure
- See Postrenal Failure Causes
- See Medication Causes of Postrenal Failure
- Benign Prostatic Hyperplasia (BPH)
- Urethral stricture
- Nephrolithiasis
- Risk Factors
- See Acute Renal Failure Risk (Nephrotoxicity Risk)
- History
- Medications (new or increased dose)
- See Drug-induced Nephrotoxicity
- See Intravenous Contrast Related Acute Renal Failure
- Trauma or myalgias
- See Rhabdomyolysis Causes
- Fluid status
- Dehydration
- Gastroenteritis
- Diuresis
- Diabetic Ketoacidosis
- Hemorrhage
- Burn Injury
- Third spacing (e.g. Ascites in Cirrhosis)
- Fluid Overload (e.g. edema in CHF)
- Infections
- See Infectious Causes of Acute Interstitial Nephritis (includes miscellaneous causes)
- See Infectious Causes of Glomerulonephritis
- See Acute Poststreptococcal Glomerulonephritis
- Symptoms: Severe Kidney Injury
- Fatigue
- Anorexia
- Nausea or Vomiting
- Weight gain
- Edema
- Confusion (uremic encephalopathy)
- Signs: Clinical Clues to Kidney injury cause
- Cardiovascular exam
- Lower extremity edema
- Congestive Heart Failure
- Nephrotic Syndrome
- Skin turgur
- Tenting in dehydration
- Abdominal exam
- Abdominal Aortic Aneurysm
- Pulsatile mass
- Abdominal bruit
- Abdominal distention
- Ascites
- Pelvic mass
- Prostate enlargement
- Distended Bladder
- Skin
- Rash of drug-induced Interstitial Nephritis
- Palpable Purpura
- Vasculitis
- Non-palpable Purpura
- Thrombotic Thrombocytopenic Purpura (TTP)
- Hemolytic Uremic Syndrome (HUS)
- Livido reticularis
- Spider angioma or caput medusae (Cirrhosis)
- Stages
- Stage 1
- Serum Creatinine increased >1.5-2x baseline (or >0.3 mg/dl increase) or
- Urine output <0.5 ml/kg/hour for >6 hours
- Stage 2
- Serum Creatinine increased >2-3x baseline or
- Urine output <0.5 ml/kg/hour for >12 hours
- Stage 3
- Serum Creatinine increased >3x baseline or
- Serum Creatinine >4.0 mg/dl and acute increase of at least 0.5 mg/dl
- Urine output <0.3 ml/kg/hour for >24 hours (or anuria for 12 hours)
- Requires renal replacement therapy (Dialysis)
- Labs
- Renal Function: Criteria for Acute Renal Failure
- See Stages above
- Serum Creatinine rises >0.3 mg/dl on 2 contiguous days or
- Serum Creatinine rises >0.5 mg/dl or
- Serum Creatinine rises >1.5 fold above baseline or
- Calculated GFR falls >50% below baseline
- Serum electrolytes
- Serum Potassium (Hyperkalemia)
- Serum Sodium
- Serum bicarbonate (Metabolic Acidosis)
- Serum Calcium
- Serum Phosphorus
- Serum Magnesium
- Fractional Excretion of Sodium (FENa)
- Requires urine sample prior to IV fluids and Diuretics
- FENa >2%: Intrinsic renal disease (e.g. Acute Tubular Necrosis)
- Falsely elevated FENa if on Diuretics
- Consider Fractional Excretion of Urea (FEUrea) if on Diuretics
- FENa <1%: Prerenal Failure
- Kidney still able to concentrate urine
- Not specific for prerenal causes (see FeNa)
- Fractional Excretion of Urea (FEUrea)
- Complete Blood Count (CBC)
- Acute Hemolytic Anemia
- Obtain Serum Bilirubin fractionated, serum LDH, Haptoglobin and Peripheral Smear (see below)
- May suggest Hemolytic Uremic Syndrome or Thrombotic Thrombocytopenic Purpura
- Platelets decreased in uremic Platelet Dysfunction
- May be accompanied with bleeding, Purpura
- Eosinophils increased in interstitial disease
- Autoimmune Testing for Glomerular Disease (Glomerulonephritis)
- Antinuclear Antibody (ANA)
- Antiglomerular basement membrane Antibody
- Antineutrophil Cytoplasmic Antibody (ANCA)
- See Small Vessel Vasculitis
- Antistreptolysin O
- Poststreptococcal Glomerulonephritis
- Complement Level
- Low in some causes of Acute Glomerulonephritis
- Percutaneous Renal Biopsy
- Indicated for Glomerular or Interstitial disease
- May be urgent in certain cases with rapid progression, oliguria or positive urine sediment
- Consult with Nephrology early when intrinsic Acute Kidney Injury is considered
- Glucocorticoids and other immunosuppressants as well as plasmophoresis may be indicated based on biopsy
- Labs: Urinalysis with Urine sediment examination
- Most important single test in identifying Acute Kidney Injury cause
- Urine Specific Gravity
- Prerenal Failure: Specific Gravity >1.020
- Intrarenal Failure: Specific Gravity 1.010 - 1.020
- Vascular disease
- Urine RBCs often present
- Glomerulonephritis, Vasculitis or Multiple Myeloma
- Urine RBCs and red cell casts
- Granular casts
- Proteinuria (esp. >3 grams)
- Interstitial Nephritis (includes drug hypersensitivity)
- Pyuria
- Eosinophils
- White Blood Cell casts and Eosinophil casts
- Tubular Necrosis
- Pigmented granular casts
- Renal tubular epithelial cells
- Granular casts
- Prerenal Failure
- Hyaline Casts
- Rhabdomyolysis
- Orthotolidine positive on Urine Dipstick with negative microscopy for Red Blood Cells
- Labs: Additional to consider if indicated
- Serum Protein Electrophoresis (SPEP) and Urine Protein electrophoresis (UPEP)
- Multiple Myeloma
- Uric Acid
- Postrenal Failure
- Serum Creatine Phosphokinase (CPK) and serum myoglobin
- Rhabdomyolysis
- Blood Cultures
- Endocarditis
- HIV Test
- HIV Nephropathy
- Metabolic Acidosis with increased Anion Gap and increased Osmolar Gap
- Acute ingestion (Ethylene gylcol, Methanol)
- Peripheral Smear for Hemolysis
- Autoimmune Vasculitis (e.g. TTP, HUS, SLE)
- Imaging: Bedside Ultrasound
- See Inferior Vena Cava Ultrasound for Volume Status
- See Echocardiogram in Congestive Heart Failure (and Echocardiogram)
- See Abdominal Aorta Ultrasound
- See Bladder Ultrasound
- Evaluate for post-void residual urine >100 ml (Bladder scan, Ultrasound or catheter)
- See Renal Ultrasound
- Obtain formal diagnostic renal Ultrasound in most patients
- Intrarenal Failure: May show parenchymal abnormality
- Postrenal Failure: Hydronephrosis
- Evaluation
- Step 1: Confirm Acute Kidney Injury criteria
- See Creatinine under labs above (as well as stages)
- Distinguish from Chronic Kidney Disease with normal fluctuation
- Step 2: Assess Urine output
- No oliguria
- Go to step 3
- Oliguria
- Acute Prerenal Failure
- Fractional Excretion of Sodium (FENa) <1%
- Distinguish volume overload (e.g. CHF) from Dehydration
- Acute Intrinsic Renal Failure or Postrenal Failure
- Fractional Excretion of Sodium (FENa) <1%
- Go to step 3
- Step 3: Renal Ultrasound
- Hydronephrosis
- Postrenal Failure
- Small Kidneys bilaterally
- Acute on Chronic Renal Failure
- Kidneys of normal size
- Go to step 4
- Step 4: Urinalysis
- Interpret urine sediment for cause of renal parenchymal condition (see Urinalysis above)
- Step 5: Additional evaluation
- See specific labs as above
- Management
- See Acute Renal Failure Management
- Prognosis
- See Acute Kidney Injury Prognosis
- Prevention
- See Prevention of Kidney Disease Progression
- See Intravenous Contrast Related Acute Renal Failure
- Resources
- Acute Kidney Injury Guidelines
- http://www.renal.org/clinical/guidelinessection/AcuteKidneyInjury.aspx
- Reference:
- Anderson (8/15/1993) Hospital Practice, p. 61-75
- Meyer (2007) N Engl J Med 357(13): 1316-25 [PubMed]
- Needham (2005) Am Fam Physician 72:1739-46 [PubMed]
- Rahman (2012) Am Fam Physician 86(7): 631-9 [PubMed]
- Singri (2003) Acute Renal Failure 289:747-51 [PubMed]
- Wilkes (1986) Am J Med 80:1129-36 [PubMed]