A commonly ordered test to diagnose a specific type of kidney disease has very little evidence showing diagnostic value, according to a recent review of the medical literature led by researchers at the University of Pittsburgh School of Medicine.
The results, published recently in the Journal of Hospital Medicine, found that urine eosinophils are too insensitive and nonspecific to confirm or exclude the diagnosis of acute interstitial nephritis (AIN) in patients with acute kidney injury.
Why was this study necessary?
A. We waste a lot of money across the United States ordering ineffective and unnecessary diagnostic tests. In response to this, the American College of Physicians began its High Value Care initiative in 2010 to help physicians improve patient outcomes while simultaneously reducing health care system waste. We noticed that urine eosinophils, a diagnostic test nephrologists know has very low diagnostic value for AIN, was still commonly ordered by many non-nephrology providers. So, we decided to review the literature and summarized the evidence strongly arguing against using this test.
What are the highlights?
A. Previous studies have shown that urine eosinophils were useful as a biomarker for AIN. However, newer and more focused studies show that the sensitivity and specificity of urine eosinophils is pretty poor.
Did anything surprise you?
A. The poor quality of the original studies supporting the use of urine eosinophils. These studies had a small number of patients and lacked biopsy confirmation of AIN. It is important that the patients we study with a disease have the disease in question. The diagnosis of AIN in these studies was done on “clinical grounds” only, without biopsy confirmation.
What happens next?
A. Doctors need to strongly consider whether they should stop ordering this test. Most of us nephrologists are well-aware of this, but unfortunately other physicians and health providers are still ordering it and trust the results. Sometimes, this means that if the test is positive, they will discontinue drugs that are important for the patient because they think the drug is causing kidney problems, or they stop looking for a different cause of acute kidney injury. If the test is negative, they rule out AIN and the patient continues on drugs that can be potentially harmful.