#NephMadness 2021: Urine Microscopy Primed for Resurgence
Jay R. Seltzer @jrseltzer
Jay Seltzer is currently Chief of Nephrology at Missouri Baptist Medical Center in St. Louis. He served an internal medicine residency and nephrology fellowship at Barnes-Jewish Hospital at Washington University School of Medicine, St. Louis, and was previously faculty in the Renal Division at Washington University School of Medicine. He is a former member of the ISNeducation Social Media Team, and is a current faculty member of GlomCon edu. He has a special interest in urine microscopy and glomerular disease.
Microscopic examination of urinary sediment is an integral part of laboratory testing in patients with kidney disease and provides valuable diagnostic information to the clinician.
It’s amazing how far urine analysis has come since the days of Pisse Prophets and the matula. We now have at our disposal microscopes capable of various illumination modalities (brightfield, darkfield, phase-contrast, and polarization), supravital stains to facilitate identification of cells, casts, and lipids, and the ability (by simply “looking” at the urine under the microscope) to broadly determine the presence (or absence) of glomerulonephritis and acute tubular injury.
Why then is urine microscopy not more widely performed by nephrologists? I imagine some nephrologists rely solely on a central laboratory report and no longer perform urine microscopy themselves. Perhaps this is a result of time constraints, or lack of available equipment and supplies. In some cases it may be due to a lack of experience identifying cellular elements and casts in the sediment. Despite advances in laboratory automation, including flow cytometry and digital imaging, an experienced nephrologist is usually better at identifying important elements (such as tubular epithelial cells, acanthocytes, and cellular casts) than laboratory personnel and automated urine analyzers. Indeed most laboratories do not report the presence of acanthocytes or lipids in the urine at all.
Accurate urinary sediment findings may facilitate a diagnosis of glomerulonephritis, interstitial nephritis, or ATN at the time of initial consultation and prevent unnecessary testing and delays in diagnosis and treatment. Just as blood tests and imaging studies do not obviate the need for a history and physical exam, a laboratory performed urinalysis is not a substitute for a focused evaluation of the urinary sediment by the nephrologist. Perhaps no one summarized this better than Norman Levinsky in his 1967 “Disease-a-Month” article “The Interpretation of Proteinuria and the Urinary Sediment”:
“A renal consultant has been defined as a physician who does the urinalysis himself. Like most aphorisms, this definition is somewhat oversimplified but contains important elements of truth. The increasing availability of newer and more sophisticated techniques such as … [serologic testing] and renal biopsy have greatly improved diagnostic precision. Nevertheless, skillful interpretation of proteinuria and the urinary sediment is still a crucial step in the differential diagnosis of renal disease. Because it contains elements derived from the kidney itself, the sediment can provide important clues to the nature of a pathologic process in the renal parenchyma. Not the least of the virtues of urinalysis is that urine can be obtained without the pain or danger to the patient which occasionally complicates the use of other diagnostic techniques. It is, therefore, distressing to a nephrologist to see how often urinalysis is neglected or performed casually. Expert internists who, faced with a problem in cardiac diagnosis, consider it mandatory to listen to the heart and to read electrocardiograms personally will often relegate urinalysis to paramedical personnel, even when renal disease is suspected. In the clinical laboratory, very often, urinalysis is considered as uninteresting or unimportant. Hence, it may be late in the day before the urine is subjected to casual examination by a disinterested technician. Back comes the “rubber stamp” urinalysis report to the physician: occasional red blood cells, occasional white blood cells, a few hyaline casts. Since the results of urinalysis appear to be identical in all forms of renal disease the physician becomes convinced that urinalysis is of little value and is not worth his personal attention. On the contrary, urinalysis nearly always reveals whether renal parenchymal disease is present and usually provides important clues to the diagnosis.”
In this year’s NephMadness the Liquid Biopsy region is well represented by strong teams, but which one will move on in the competition?
Urine Microscopy for ATN has a reliable record, useful in assessing the likelihood of ATN as the cause of AKI, however Urine Microscopy for GN has the power to differentiate glomerular from non-glomerular hematuria (often preventing unnecessary GU procedures) and can determine the need for empiric therapy. In this matchup Urine Microscopy for GN should win.
While the players Sternheimer-Malbin and Sudan III produce higher resolution images (under brightfield illumination), and facilitate identification of some of the formed elements in the sediment, the Staining Techniques team is no match for Microscopy Techniques! The illuminating players on the Microscopy Techniques team include Brightfield, Darkfield, Phase-contrast (Nobel Prize winner in Physics in 1953), and Polarization. These modalities alter the path of light in different ways to allow visualization and identification of all of the formed elements. I admit the Staining Techniques team looks good in pictures, however they lack the versatility of the Microscopy Techniques team which covers the whole court. Staining is of little value in the identification of crystals and cholesterol, it interferes with phase-contrast image formation, is at times prone to precipitation artifact, and may facilitate pseudocast formation.
Liquid Biopsy region’s teams are long overdue as players in NephMadness and I believe Microscopy Techniques has the utility, versatility, and clinical prowess to win not only the region, but the entire competition. It is rare to find a safe, inexpensive and readily available diagnostic technique that can provide such valuable diagnostic and therapeutic insight in cases of AKI and proteinuria. Urine Microscopy is primed for a resurgence in the care of patients with kidney disease.
– Guest Post written by Jay R. Seltzer @jrseltzer
As with all content on the AJKD Blog, the opinions expressed are those of the author of each post, and are not necessarily shared or endorsed by the AJKD Blog, AJKD, the National Kidney Foundation, Elsevier, or any other entity unless explicitly stated.
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