An automated approach to body fluid analysis

Body fluid cell counts are a routine laboratory test that provides valuable information to clinicians for diagnosing and treating a wide variety of medical conditions. Traditionally, body fluid counts have been performed by manually counting RBCs and nucleated cells under a microscope using a hemacytometer. However, this can be a subjective and an extremely labor-intensive process. Laboratories now have options for automating cell counts. Of particular interest is the availability to perform automated cell counts on urinalysis platforms.

One option that has enabled labs to overcome the labor burdens body fluid analysis testing presents has been running body fluid cell counts on hematology analyzers. Automated body fluids analysis has improved accuracy and precision and is more rapid and less labor-intensive than manual cell counts. However, hematology analyzers may not be the preference for some labs in all situations where cell counts are needed. Typically, automated hematology analyzers are not used for clear and colorless cerebrospinal fluids with low cellular counts because of poor reproducibility and high background counts at medically important clinical decision limits of 0 to 5 cell/µL for adults. Other types of specimens that laboratories may not want to run on hematology analyzers are purulent and flocculent specimens, because there is concern that those specimens could clog flow cells or apertures. Additionally, crystals in synovial fluids may cause a falsely increased count and may need to be confirmed with the manual count.¹ 

In recent years, an alternative solution for automated body fluid cell counting has emerged through the addition of body fluid analysis on automated urinalysis analyzers. Technological advances in hardware and software engineering have developed instruments with expanded analytical capabilities that enable processing multiple specimen types including urine, CSF, peritoneal fluid, pleural fluid, synovial fluid, and lavages on a single analyzer. Unlike hematology analyzers, which use particle counting and flow cell technology, automated urinalysis analyzers use digital imaging to perform counts. When digital imaging technology is used, there is reduced interference from background counts. As a result, urine analyzers that use digital imaging have been judged to perform better than hematology analyzers with low cell counts.^1-4

Modern urine analyzers have significantly improved the efficiencies and productivity in today’s clinical laboratory by drastically reducing the labor burden associated with manual urinalysis and adding the benefit that the same technology used for automated urine microscopy can be used for body fluid analysis. Conceptually, urinalysis and body fluid analysis together on the same platform may seem like an orthogonal process; however, it’s actually the most practical and advantageous. 

Increasingly, larger hospitals and clinical reference laboratories have made the leap from manual urinalysis—dipstick and microscope—to automated urinalysis, which offers both urine chemistry and urine microscopy as combined systems. Performing the automated body fluid counting on the same analyzer as the urinalysis can increase the testing volume, which may help justify the cost of an automated workcell, not only for larger labs but also for low-volume laboratories which may also be performing manual urine microscopies. 

According to an article by T. Kickler et al., published in 2009, using a urinalysis analyzer for body fluid testing demonstrated excellent correlation with the manual hemacytometer method.² The authors found that the analyzer removed background interference and was linear to zero. Moreover, the article reported that while samples with higher cell counts required a substantial amount of time and labor using the manual technique, the analyzer handled samples with ease. The authors concluded that when encompassing result equivalency along with labor and time savings, using an automated urinalysis analyzer was a viable alternative to the hemacytometer.

Using a parallel process with urinalysis, automated microscopy enables analysis of eight different types of body fluids: CSF, synovial, pleural, peritoneal, peritoneal dialysate, peritoneal lavage, pericardial, and general serous fluid. For each body fluid type, automated microscopy can deliver true cell-count standardization and onscreen imaging of bacteria and crystals and can automatically differentiate red blood cells and nucleated white blood cells. Not surprisingly, processing body fluids on a urinalysis platform can benefit numerous areas of the lab. Not only does this help consolidate workflow; it also streamlines the review process by having results available from the same system and saves time. 

Until the advent of electronic cell counters, the unique properties of synovial fluid mandated labor-intensive and time-consuming manual techniques. While automated cell counters have improved proficiency and workflow productivity in clinical laboratories, a frequent problem encountered with these instruments is the high number of misread samples. Due to the elevated background counts common with several types of body fluid samples, synovial fluids in particular, errant increases of low cell counts often trigger returning to the microscope to manually verify result accuracy. Current technology, however, has cleared such technical hurdles and correctly analyzes samples with both low and high cell counts in virtually every type of body fluid, including synovial fluid, delivering excellent correlation with manual methodology. In addition, both crystals and bacteria are presented in a given fluid type, allowing the user through the edit function to categorize accordingly. 

Accurate and fast urinalysis and body fluid results lead to improved turnaround time for the lab and assist in accelerating ED admit and discharge decisions. In today’s clinical laboratory, improved efficiencies and enhanced productivity are essential. Merging urinalysis and body fluid testing, using a single automated platform, streamlines processes and optimizes labor resources, resulting in proven, valuable benefits not only for the lab but for the clinician and ultimately the patient.