Each of the following is associated with acute tubular necrosis, except
ExplanationAcute tubular necrosis is classified as a “renal” (e.g., not prerenal or postrenal) cause of acute kidney injury. Diagnosis is made by a fractional
excretion of sodium >3%, greater than expected urine sodium concentration with low osmolality and presence of muddy casts on urinalysis. A sensitive
indicator of tubular function is sodium handling because the ability of an injured tubule to reabsorb sodium is impaired, whereas an intact tubule can maintain this resorptive capacity. If the patient has tubular damage for any reason, the urinary sodium will be greater than expected. Keep in mind that the
use of diuretics, however, can complicate the interpretation of these results. Low urine flow, concentrated urine, or an acidic environment can contribute to
the formation of hyaline casts, pointing to hypovolemia and prerenal failure .
