Increased prevalence of acute interstitial nephritis: more disease or simply more detection?

Acute interstitial nephritis (AIN) is the second leading cause of acute, intrinsic kidney disease [1]. Unlike acute tubular necrosis, the most common cause of intrinsic kidney injury, AIN is known to have a high potential for reversibility if identified early [2]. The diagnosis of AIN is often made empirically based on the clinical presentation (e.g. a case of acute kidney injury (AKI) accompanied by a history of rash and fever, peripheral eosinophilia and a urine devoid of protein), yet a true diagnosis of AIN can only be established by a renal biopsy. Indeed, because AIN most commonly occurs in the absence of supportive clinical or laboratory findings, the importance of kidney biopsy to firmly diagnose AIN as the cause of AKI cannot be understated. A biopsy not only confirms the pathologic diagnosis but can also provide information on the severity of the injury, activity versus chronicity of the lesion, and the presence of other significant glomerular or vascular abnormalities that may influence treatment decisions [3].