Figure 1215

Urinalysis in acute renal failure (ARF). A normal urinalysis suggests a prerenal or postrenal form of ARF; however, many patients with ARF of postrenal causes have some cellular elements on urinalysis. Relatively uncommon causes of ARF that usually present with oligoanuria and a normal urinalysis are mannitol toxicity and large doses of dextran infusion. In these disorders, a "hyperoncotic state" occurs in which glomerular capillary oncotic pressure, combined with the intratubular hydrostatic pressure, exceeds the glomerular capillary hydrostatic pressure and stop glomerular filtration. Red blood cells (RBCs) can be seen with all renal forms of ARF. When RBC casts are present, glomerulonephritis or vasculitis is most likely.

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