Many other diseases of the kidney are associated with liver disease and must be excluded before making a diagnosis of hepatorenal syndrome. Individuals with pre-renal kidney failure do not have damage to the kidneys, but as in individuals with HRS, have kidney dysfunction due to decreased blood flow to the kidneys. Also, similarly to HRS, pre-renal kidney failure causes the formation of urine that has a very low sodium concentration. In contrast to HRS, however, pre-renal kidney failure usually responds to treatment with intravenous fluids, resulting in reduction in serum creatinine and increased excretion of sodium. Acute tubular necrosis (ATN) involves damage to the tubules of the kidney, and can be a complication in individuals with cirrhosis, because of exposure to toxic medications or the development of decreased blood pressure. Because of the damage to the tubules, ATN affected kidneys usually are unable to maximally resorb sodium from the urine. As a result, ATN can be distinguished from HRS on the basis of laboratory testing, as individuals with ATN will have urine sodium measurements that are much higher than in HRS; however, this may not always be the case in cirrhotics. Individuals with ATN also may have evidence of hyaline casts or muddy-brown casts in the urine on microscopy, whereas the urine of individuals with HRS is typically devoid of cellular material, as the kidneys have not been directly injured. Some viral infections of the liver, including hepatitis B and hepatitis C can also lead to inflammation of the glomerulus of the kidney. Other causes of kidney failure in individuals with liver disease include drug toxicity (notably, the antibiotic gentamicin) or contrast nephropathy, caused by intravenous administration of contrast agents used for medical imaging tests.