Acute tubular necrosis: A severe form of acute renal failure that develops in people with severe illnesses (such as sepsis) or with very low blood pressure. Patients may need dialysis. Kidney function often improves if the underlying disease is successfully treated. Abbreviated ATN. Many times the term is used synonymously with the term acute renal failure (ARF). Generally, ATN would refer to acute renal failure of the renal category where there has been damage to the filtering unit of the kidney itself (glomerulus and its associated tubular network).