<prompt> Which of the following is most likely cause of ARF in patient with renal failure index 1?Acute glomerulonephritisCongestive cardiac failureBilateral acute pyelonephritisTTP  <response>: Ans. b Congestive Cardiac Failure Ref. Harrison 18th p 1649; Table 260-3CAUSES OFARFA. Diseases that cause renal hypoperfusion without compromising the integrity of renal parenchyma prerenal ARF, prerenal azotemia -55;B. Diseases that directly involve renal parenchyma intrinsic renal ARF, renal azotemia -40; andC. Diseases associated with urinary tract obstruction postrenal ARF, postrenal azotemia -5.CAUSES OFARFPrerenal causes Volume depletion Decreased effective circulatory volume e.g., heart failure, liver failure, Treatment with NSAIDs or ACE inhibitorsIntrinsic renal ARF Diseases involving large renal vessels- Renal artery thrombosis- Atheroembolism- Renal vein thrombosis Diseases of small vessels and glomeruli- Glomerulonephritis vasculitis- Hemolytic-uremic syndromethrombotic thrombocytopenic purpura- Malignant hypertension ARF mediated by ischemia or toxins ATN- Ischemia- Exogenous toxins, e.g., Recent radiocontrast study, nephrotoxic antibiotics or anticancer agents often coexistent with volume depletion, sepsis, or chronic renal insufficiency- Endogenous toxins, e.g., history suggestive of rhabdomyolysis seizures, coma, ethanol abuse, trauma, History suggestive of hemolysis blood transfusion- History suggestive of tumor lysis recent chemotherapy, myeloma bone pain, or ethylene glycol ingestion Acute diseases of the tubulointerstitium- Allergic interstitial nephritis- Acute bilateral pyelonephritis Diagnostic IndexTypical findings in ARF PrerenalIntrinsic RenalFractional excretion of sodium UNa x Pcr---PNa x Ucrx 10011Urine sodium concentration mmolL1020Urine creatinine to plasma creatinine ratio4020Urine urea nitrogen to plasma urea nitrogen ratio83Urine specific gravity1.020-1.010Urine osmolality mOsmkg H20500-300Plasma BUNcreatinine ratio2010-15Renal failure index11UNa---UcrPcr Urinary sedimentHyaline castsMuddy brown granular castsAlso know:More than 70 of kidney function must be lost before features of renal failure become evident 