Quality in urine microscopy: The eyes of the beholder

URINE MICROSCOPY: THE NEPHROLOGIST’S ROLE

The tools used in urine microscopy have advanced significantly since its advent. But not all advances have led to improved patient care. Laboratories have trained technicians to perform urine microscopy. Analyzers can identify basic urinary structures using algorithms to compare them against stored reference images. More important, urine microscopy has been categorized by accreditation and inspection bodies as a “test” rather than a physician-performed competency. As such, definitions of quality in urine microscopy have shifted from the application of urinary findings to the care of the patient to the reproducibility of identifying individual structures in ways that can be documented with quality checks performed by nonclinicians. And since the governing bodies require laboratories to adhere to burdensome procedures to maintain accreditation (eg, the US Food and Drug Administration’s Clinical Laboratory Improvement Amendments), many hospitals have closed nephrologist-based urine laboratories.

This would be acceptable if laboratory-generated reports provided information equivalent to that obtained by the nephrologist. But such reports rarely include anything beyond the most rudimentary findings. In these reports, the red blood cell is not differentiated as dysmorphic or monomorphic. All casts are granular. Crystals are often the highlight of the report, usually an incidental finding of little relevance. Phase contrast and polarization are never performed.

Despite the poor quality of data provided in these reports, because of increasing regulations and time restrictions, a dwindling number of nephrologists perform urine microscopy even at teaching institutions. In an informal 2009 survey of nephrology fellowship program directors, 79% of responding programs relied solely on lab-generated reports for microscopic findings (verbal communication, Perazella, 2017).

There is general concern among medical educators about the surrendering of the physical examination and other techniques to technology.^7,8 However, in many cases, such changes may improve the ability to make a correct diagnosis. When performed properly, urine microscopy can help determine the need for kidney biopsy, differentiate causes of acute kidney injury, and help guide decisions about therapy. Perazella showed that urine microscopy could reliably differentiate acute tubular necrosis from prerenal azotemia.⁹ Further, the severity of findings on urine microscopy has been associated with worse renal outcomes.¹⁰ At our institution, nephrologist-performed urine microscopy resulted in a change in cause of acute kidney injury in 25% of cases and a concrete change in management in 12% of patients (unpublished data).

With this in mind, it is concerning that the only evidence in the literature on this topic demonstrated that laboratory-based urine microscopy is actually a hindrance to its underlying purpose in acute kidney injury, which is to help identify the cause of the injury. Tsai et al¹¹ showed that nephrologists identified the cause of acute kidney injury correctly 90% of the time when they performed their own urine microscopy, but this dropped to 23% when they relied on a laboratory-generated report. Interestingly, knowing the patient’s clinical history when performing the microscopy was important, as the accuracy was 69% when a report of another nephrologist’s microscopy findings was used.¹¹

APPLYING RESULTS TO THE PATIENT

The purpose of urine microscopy in clinical care is to identify and understand the findings as they apply to the patient. When viewed from this perspective, the renal patient is clearly best served when the nephrologist familiar with the case performs urine microscopy, rather than a technician or analyzer in remote parts of the hospital with no connection to the patient.

Advances in technology or streamlining of hospital services do not always produce improvements in patient care, and how we define quality is integral to identifying when this is the case. Quality checklists can serve as guides to safe patient care but should not replace clinical decision-making. Direct physician involvement with our patients has concrete benefits, whether taking a history, performing a physical examination, reviewing radiologic images, or looking at specimens such as urine. It allows us to experience the amazing pathophysiology of human illness and to understand the nuances unique to each of our patients.

But most important, it reinforces the need for the direct bond, both emotional and physical, between us as healers and our patients.