Are we performing too many tests for acute kidney injury?

Patients with acute kidney injury (AKI) undergo a large number of tests, many of which are of limited clinical value, reports a study in BMC Nephrology (5).

The retrospective study included 5731 AKI episodes in 4903 adult inpatients at an academic medical center over 1 year. Rates of test performance and abnormal results were calculated for various urine, blood, radiologic, and pathology tests, including differences by AKI stage. Diagnostic yield was determined by manual review of electronic medical records.

The most common known etiologies of AKI were ischemic acute tubular necrosis, prerenal azotemia, nephrotoxic acute tubular necrosis, and cardiorenal syndrome. The most frequently ordered tests were urinalysis and automated urine sediment examination. Ultrasound was performed in 10 percent of patients, and biopsy was performed in 0.5 percent of patients.

For nearly all tests, frequency increased with higher AKI stage. Some tests were more likely to show abnormal results at higher AKI stages, but others were not. The frequency of abnormal results ranged from 0 percent for antiglomerular basement membrane testing to 71 percent for urine protein tests.

For many tests, diagnostic yield was low. Selected blood and urine tests had low effects on AKI diagnosis and management, but radiologic tests were more likely to show clinical utility. The ratio of number of tests ordered to number of tests with clinical utility ranged from 5 for abdominal/pelvic computed tomography to 60 for urine eosinophils.

The optimal approach to diagnostic evaluation of AKI has not been defined; many different tests are available. This new study questions the diagnostic value of many of the large number of tests used in patients with AKI.

Many tests have limited clinical utility, even when the results are abnormal or positive. Leaf et al. (5) highlight the need to develop tests that provide “reliable or actionable data” for AKI diagnosis and management [Leaf DE, et al. Excessive diagnostic testing in acute kidney injury. BMC Nephrol 2016; 17:9].