Lab findings in Pre-renal and ARF

Lab Findings in Prerenal Azotemia and ARF

• • With hypoperfusion, the urine is typically concentrated with an osmalilty >500 mOsm/kg and a high specific gravity >1.020.

  • In ATN, concentrating ability is lost and the urine is usually isomolar to the serum. In the blood, the ratio of BUN to creatinine is normally <20:1 and an elevation is consistent with hypovolemia.

  • BUN/Cr. An ▲ BUN relative to Cr may also be due to increased urea production that occurs with hyperalimentation (high-protein), glucocorticoid therapy, and GIB.

  • FeNa has limited utility when ARF is superimposed on CKD.

Serologic testing can further delineate the cause of ARF

• • Antiglomerular basement membrane, Ab in Goodpasure's syndrome.

  • ANCA-ab (C-ANCA) in microscopic PAN or Wegener's syndrome

  • ANA in SLE