Validating the Use of Urine Sediment Analyzers
Manual microscopy on positive dipstick specimens can present quality risk, and even result in patient misdiagnosis. According to a recent article in CAP TODAY, many laboratories are using automated urine sediment analyzers to ensure accurate diagnosis.
To perform urine sediment analysis, the renal laboratory at Mayo Clinic in Rochester, Minn., uses Beckman Coulter’s Iris iQ200, which also includes an automated dipstick reader. And, as the result of a three-way correlation of that instrument, the Sysmex UF-1000i, and manual microscopy, the laboratory uses the Sysmex for bacteria quantification, says nephrologist John Lieske, M.D., professor of medicine and medical director of the Mayo renal testing laboratory.
According to Dr. Lieske, “The correlation study showed the Sysmex UF-1000i was excellent for quantifying bacteria, and for predicting a positive culture, it was quite good.” He and colleagues also conducted a study that established bacteria cutoffs for a positive urine culture. In screening urines, the laboratory now uses the cutoffs to determine whether to do a culture.
The Mayo Clinic renal laboratory uses the Iris iQ200 to screen out fairly normal urines, which represents about two-thirds of the samples. According to the article, the laboratory first tests the urine specimens for protein on a Roche chemistry analyzer. Those containing abnormal amounts of total protein “get shunted to the manual microscopy,” Dr. Lieske says, as they are “quite likely to have pathological elements such as dysmorphic red cells or casts.”
The rest of the samples go to the iQ200. According to Dr. Lieske, "The instrument takes pictures of urine as it goes by and flags what it finds. It saves the pictures, and the technician takes a look and verifies whether he or she sees anything pathologic. The technician can also reclassify elements if needed.”
The technicians manually review anything except hyaline casts or common urinary crystals. “Hyaline casts are not considered pathologic in and of themselves,” he says. “But you have to differentiate those from ones that, say, have red cells in them. If they did, then they would be red cell casts,” which are seen in people with glomerulonephritis. As another example, “You can have fatty casts with nephrotic syndrome.”