Signs and Symptoms
- Clinicians need to search for specific signs of underlying renal disease.
- Severe anemia due to hemolytic-uremic syndrome
- Butterfly rash on face/musculoskeletal involvement in systemic lupus erythematosus
- Purpuric rash over buttocks and extensor surface of lower extremity in Henoch-Schönlein purpura.
- Palpable kidney may be due to:
- Renal vein thrombosis
- Polycystic kidney disease
- Multicystic dysplastic kidney
- Hydronephrosis
- Palpable bladder with weak urine stream or dribbling suggests obstruction.
- Sacral tuft of hair or myelomeningocele may be seen with neurogenic bladder (can cause obstructive uropathy/postrenal oliguria or anuria).
- Symptoms of prerenal cause
- Vomiting
- Diarrhea
- Hemorrhage
- Sepsis
- Decreased oral intake
- Increased thirst
- Palpitations
- Fatigue
- Clinical signs of dehydration
- Weight loss
- Symptoms of hypovolemia (ie, prerenal pathology)
- Tachycardia
- Dry mucous membranes
- Sunken eyes
- Orthostatic blood pressure changes
- Decreased skin turgor
- Hypotension
- Symptoms of intrinsic renal disease
- Gross hematuria
- Pharyngitis or impetigo a few weeks before the onset of gross hematuria
-
Hypertension
-
Edema
- Bloody diarrhea
- Often precedes hemolytic-uremic syndrome
- Younger children, particularly infants: signs of congestive heart failure
- Hepatomegaly
- Gallop rhythm
- Pulmonary edema
- Symptoms of systemic vasculitis (eg, systemic lupus erythematosus)
- May see history of fever, joint pains, and skin rash
- Recurrent sinusitis or lower respiratory tract infections may suggest Wegener granulomatosis.
- Hemoptysis may indicate pulmonary-renal syndrome, due to either:
- Goodpasture syndrome
- Microscopic polyangiitis
Diagnostic Approach
- Thorough history and physical examination are important in identifying the cause of oliguria or anuria.
- Comprehensive physical examination is key to assessing severity of the disease process and possible cause.
- In prerenal and postrenal ARF, early diagnosis and prompt treatment often result in quick recovery.
- Detailed history of recent or ongoing long-term medication use is important for excluding possible interstitial nephritis.
- In neonates, history of umbilical artery catheterization implies renal artery thrombosis.
- Family history is helpful in diagnosing such conditions as diabetes insipidus and polycystic kidney disease.
Laboratory Findings
- Risk factors, history, and results of physical examination will help in the selection of appropriate laboratory tests.
- Urinalysis is the most important noninvasive diagnostic test.
- Thorough examination of a freshly voided or bladder-catheterized urine sample helps distinguish prerenal from renal causes.
- Normal or near-normal urinalysis, with few cells, few or no casts, or little or no proteinuria, is seen in prerenal disease, obstruction, and some cases of acute tubular necrosis.
- A sample showing muddy-brown granular casts and epithelial cell casts strongly suggests acute tubular necrosis.
- Erythrocyte casts are diagnostic of glomerulonephritis.
- Proteinuria indicates glomerular disease.
- Urinary indices important for diagnosis of oliguria
- Urinary sodium
- < 10 mEq/L in oliguria resulting from intravascular volume depletion
- Neonates: prerenal disease is associated with urine sodium concentration < 20–30 mEq/L.
- Specific gravity
- > 1020 in prerenal oliguria
- Creatinine
- Urine/plasma creatinine ratio > 40 in prerenal oliguria
- Urine/plasma creatinine ratio < 20 if renal cause
- Osmolality
- Urine/plasma osmolality > 1.5 in prerenal oliguria
- Urine/plasma osmolality < 1.5 if renal cause
- Fractional excretion of sodium
- < 1% suggests reabsorption of almost all filtered sodium in response to decreased renal perfusion (prerenal).
- In acute tubular necrosis: > 2%
- Blood urea nitrogen (BUN) and serum creatinine
- In prerenal oliguria, increased BUN level is marked and the BUN/serum creatinine ratio is > 20.
- BUN/creatinine ration of 10–15 suggests intrinsic renal damage.
Imaging
- Renal ultrasonography
- Generally not indicated in children with prerenal failure from dehydration who respond promptly to fluid resuscitation
- Provides important information regarding
- Kidney size and echogenicity
- Renal blood flow
- Collecting system
- Urinary bladder
- Children with intrinsic causes
- Echogenic and slightly enlarged kidneys
- Bilateral hydronephrosis or hydroureteronephrosis and bladder wall thickening indicate obstruction of bladder outlet causing postrenal oliguria/anuria.
- Ultrasonography can detect congenital disorders, such as polycystic kidney disease and multicystic dysplastic kidney.
- Doppler examination of renal blood flow is helpful in diagnosing renal vascular thrombosis.
Classification
- Prerenal: dehydration is the most common cause of oliguria/anuria in children.
- Renal: intrinsic renal disorders, such as acute tubular necrosis and glomerulonephropathies
- Postrenal: obstruction to urinary flow in posterior urethral valves in boys
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