Investigations

• blood count ^d
• urea, electrolytes, creatinine, glucose ^a
  
  Calculate
  • urea (in mmol/L): creatinine (in mol/L) ratio ^c 
  • creatinine clearance ^d

• arterial blood gas, pH ^d
• chest X-ray ^d
• ECG ^d

• ESR, CRP
• calcium
• creatinine kinase
• blood cultures
• inflammatory screen:
  • autoantibodies: ANA, anti-dsDNA, ANCA, anti-GBM)
  • complement levels
  • cryoglobulins
  • immunoglobulins
    
    
• serum and urine electrophoresis: for myeloma, lymphoma, amyloid

• Perform a urine dipstick, and look for
  • protein ^b
  • leucocytes ^b  
  • haemoglobin ^b  

   

• Send for 
  • urine microscopy
    Look out for comments on

  • red blood cell shape ^b  
  • lymphocytes ^b  
  • eosinophils ^c
  • casts ^b  

  • culture ^d
  • biochemistry,  if trying to distinguish acute tubular necrosis from pre-renal causes ^c

• urine sodium ^c  
• urine chloride ^c  
• urine creatinine ^c  
• urine osmolality ^c
  
  Use these results to calculate
  • the fractional excretion of sodium:  ^c  
    • [Urine Na x Plasma creatinine]/[Plasma Na x Urine creatinine] x 100
  • the fractional excretion of chloride  ^c  
    • [Urine Cl x Plasma creatinine]/[Plasma CL x Urine creatinine] x 100

• Note: these indices are only valid predictors if:
  • no previous diuretics
  • previously normal renal function

   

• CT or ultrasound scan ^a  
  • Look for hydronephrosis (collecting system dilatation): most patients with hydronephrosis have obstruction

Consider inserting a central line. ^d

Ask for a nephrology opinion. ^d

• Consider performing a renal biopsy if ^c  
  • clinical signs suggestive of primary renal disease, vascular lesions or systemic disease 
  • no obvious cause for acute renal failure 
  • suspected acute interstitial nephritis or drug-induced vasculitis 
  • oligo-anuria thought due to ATN persists beyond 3 weeks without perpetuating factors