Acute interstitial nephritis (AIN) is the cause of over 15% cases of acute loss of kidney function Unlike many other causes of acute loss of kidney function, AIN is treatable with steroids if culprit is stopped in many occasions. Diagnosis of AIN is often difficult and there have been various markers in the history of AIN
Currently, AIN commonly occurs because of various non–β-lactam antibiotics, proton pump inhibitors, nonsteroidal antiinflammatory drugs, and cancer immunotherapy agents.
The classical triad of rash, fever and AKI doesn’t always exist in all cases. In addition, while seen many times, not all cases have a peripheral eosinophilia. A trend of rising eosinophils is often noted in several cases.
The classically used urine eosinophils was thrown under the bus few years ago. Yet, many still order that test that is very non specific and not sensitive for AIN.
Imaging studies such as MAG-3 scans are rarely used and not as sensitive or specific for AIN. A kidney biopsy is often needed before giving steroids. Often this is not possible due to active infection, recent infection, anticoagulation.
A recent study published in JCI shows some novel urinary markers that might be used to diagnosis AIN. In a single center, 15% of patients had AIN. Participants with AIN had consistently higher levels of urine TNF-α and IL-9 than those with other diagnoses, including acute tubular injury, glomerular diseases, and diabetic kidney disease, and those without any kidney disease. The higher the TNF and IL-9, the higher the index of renal biopsy injury. The kidney biopsies with AIN also stained highly with TNF and IL-9. In addition, the clinicians diagnosis index improved significantly with addition of these urinary markers.
AIN is a tough diagnosis to make. This study adds value in perhaps using other biomarkers that show signs of T cell activation. Is this specific for renal disease is a trend to watch? To me, there are no clinical signs that are real obvious clues. Urine eos- most useless, MAG-3 scans,- not useful. Serum eos trends- maybe useful. Urine WBCS casts and WBCS- not specific. The current study adds to the most specific findings thus far for an AIN diagnosis