Automation of Urine and Body Fluid Analysis

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Automation of Urine and Body Fluid Analysis

Learning Objectives

Key Terms1

Automation of Urinalysis

A goal of the urinalysis laboratory is to maximize productivity and testing quality while keeping costs and turnaround time at a minimum. The first reagent strip tests to determine the chemical composition of urine were developed in the 1950s in an effort to achieve these goals. Since that time, reagent strips have streamlined the chemical examination, significantly reducing the time required and increasing the number of spec-imens that can be analyzed in a given time period. Efforts next focused on ensuring consistency in reagent strip reading (e.g., color interpretation, timing), reducing the amount of specimen handling, and increasing specimen throughput. These efforts have resulted in the development of instruments that assess reagent strip results and automate evaluation of the physical characteristics of urine. In the early 1980s, automation of the microscopic examination was achieved by the development of a urine microscopy analyzer (i.e., Yellow Iris). Today, automated urine chemistry analyzers and urine microscopy analyzers are available that can be used as standalone instruments or linked together to enable a fully automated urinalysis system.

As with all technology, new analyzers and methods are constantly being developed and modified. The combinations of analyzers or urinalysis workstations available through the collaboration of manufacturers are dynamic and change with time. Note that despite our global economy, instruments that are available in Europe or Asia may not be available in the United States, and vice versa. The instruments presented in this chapter are limited to those most commonly encountered in US laboratories and one available outside the United States. Although manufacturers use the same technology for their urine chemical analyzers, the approach used for automated microscopy varies among three principles—digital flow morphology, flow cytometry, and digital microscopy using a cuvette or cell.

Urine Chemistry Analyzers

Semiautomation of the chemical examination of urine was developed to standardize the interpretation of reagent strip results. Consistent, unbiased, and accurate color interpretation was the goal when urine chemistry analyzers were developed. All reagent strip reading instruments, regardless of manufacturer, use reflectance photometry to interpret the color formed on each test pad. These semiautomated instruments require the user to properly dip the reagent strip and place it onto a platform. After this is done, the instrument automatically performs the remaining steps in the analysis: reading the reaction pads at the appropriate read time and moving the strip to a waste container.

Some manufacturers include a color compensation pad on their reagent strips. The purpose of this pad is to assess urine color and use it when interpreting the colors that develop on each reaction pad. In other words, the instrument modifies test results by essentially subtracting the contribution of urine color from the color change obtained on the test reaction pads. Note that this is possible only when reagent strip results are interpreted using an automated instrument. Consequently, depending on the intended use—manual or automated—reagent strips with or without a color compensation pad are available.

Principle of Reflectance Photometry

Reflectance photometry quantifies the intensity of the colored product produced on the reagent strip reaction pads. When light strikes a matte or unpolished surface (e.g., a reagent strip), some light is absorbed and the remaining light is scattered or reflected in all directions. The scattered light is known as diffuse reflectance. In reflectance photometers, the incident light is usually of one or more wavelengths, whereas only reflected light of a single, specific wavelength is detected. These photometers are calibrated using reflectance standards such as magnesium carbonate or barium sulfate that “completely” reflect all incident light. Because the potential colors that develop on each reaction pad dictate the wavelengths of light needed for reflectance measurements, each reflectance photometer must have a way of selecting the appropriate wavelength for each test pad. To obtain the desired wavelength, reflectance photometers use (1) polychromatic light and a series of filters to isolate specific wavelengths or (2) a series of monochromatic light sources (e.g., light-emitting diodes [LEDs]).

Reflectance measurements are performed at specific wavelengths and are expressed as percent reflectance (% R). The % R is the ratio of the test pad reflectance (Rt) compared to the calibration reflectance (Rc), multiplied by the percent reflectivity of the calibration reference, which is usually 100%.

% R=RtRc×100 Equation 16.1

image Equation 16.1

The relationship between concentration and reflectance is not linear. Therefore a microprocessor is needed to apply complex algorithms that convert the relationship to a linear one and to obtain a semiquantitative analyte value for each reaction pad on the test strip.

Semiautomated Chemistry Analyzers

The term semiautomated urinalysis indicates that an analyzer is used to interpret the commercial reagent strip results of urine when the chemical examination is performed. The term semiautomated indicates that the user performs the remaining steps of the urinalysis—physical examination of color and clarity, as well as the microscopic examination, if performed.

Numerous reagent strip manufacturers are located worldwide, and many market a reflectance photometer for use with their specific reagent strips. An example of a semiautomated instrument is shown in Fig. 16.1. All instruments are user friendly and have various display and audio prompts to aid in their operation. Most semiautomated systems require the user to (1) press a button to ready the analyzer for analysis, (2) properly dip the reagent strip into a suitable urine sample, (3) blot the strip to remove excess urine, and (4) place the strip onto an intake platform. A microprocessor controls the remaining aspects of testing: it mechanically moves the strip through the instrument. At the appropriate timed interval, reflectance readings are taken and adjusted for urine color (when a color compensation pad is included on the reagent strip). Results are stored by the microprocessor and, last, the strip is automatically moved to a waste container or manually discarded by the operator.

Patient identifiers, user identification, and the physical parameters of the urine can be manually entered into the analyzer; a barcode reader can be used to identify specimens. Typically, results print out, are stored within the analyzer, or can be transmitted to a laboratory information system (LIS). The quantity of patient and daily quality control results that can be stored on-board varies with the analyzer. Table 16.1 lists some basic features of semiautomated urine chemistry analyzers. Daily maintenance consists primarily of cleaning the transport platform and areas in contact with the reagent strips and emptying the waste container of used reagent strips.

Table 16.1

Typical Features of Semiautomated Urine Chemistry Analyzers
Tests performed Blood, leukocyte esterase, nitrite, protein, glucose, ketone, bilirubin, urobilinogen, pH, specific gravity
Measurement principle Intensity of color on reagent strip pads measured by reflectance photometry; automatic adjustments made for urine color
Sample handling User manually dips and places strip onto instrument platform
Sample ID entry User manually enters, uses a barcode reader, or downloads from LIS
Results Printout and on-board data storage; can interface to LIS
Color and clarity can be manually entered for report and printout
Daily maintenance Clean reagent strip platform; empty used reagent strip container


LIS, Laboratory information system.

Fully Automated Chemistry Analyzers

When using a fully automated urine chemistry analyzer, the user simply places labeled tubes of urine into a sample rack or carousel. Testing is initiated by pressing a button on the instrument display or automatically with placement of a sample rack. From this point on, the instrument controls movement of the specimen rack, identifies each sample, mixes it, aspirates urine using a sample probe, and dispenses it onto a reagent strip. At the appropriate read time, each reaction is read using the appropriate wavelengths of light for that specific test.

Fully automated urine chemistry analyzers can also determine the physical characteristics of urine—color, clarity, and specific gravity (SG)—however, the methods used vary. To perform urine color assessment, some manufacturers include an additional pad on the reagent strip to determine urine color by reflectance photometry; others use spectrophotometry at multiple wavelengths to assign color. Light transmittance or light scatter is used to determine urine clarity. Despite the universal availability of an SG reagent strip test, most fully automated chemistry analyzers use refractive index because of its greater accuracy. A microprocessor collates all results—color, clarity, SG, and chemistry tests—which are subsequently sent to data storage and can be printed on a report form or sent electronically to an LIS.

Automated Microscopy Analyzers

Automated urine particle analyzers assist in decreasing labor costs and increasing productivity in the urinalysis laboratory. They eliminate observer-associated variation, reduce the need for manual microscopy review, and offer results similar to those of manual microscopy.1 Because uncentrifuged urine is used, the time spent in handling and preparing concentrated urine sediment for manual microscopy is eliminated; this also reduces exposure to potential biohazards. Other benefits include increased standardization of the microscopic examination, which enhances the accuracy and reproducibility (precision) of results. Second, because these analyzers are usually interfaced to an LIS, manual data entry is decreased, which reduces the potential for transcription errors. Last, significant data storage is available in some instruments such that urinalysis results can be archived and retrieved later for consultations, continuing education, competency assessments, or training purposes (e.g., iQ200 analyzer).

Manufacturers use one of three technologies to perform automated urine microscopic analysis: (1) digital flow morphology, (2) flow cytometry, or (3) digital microscopy using a cuvette or cell.1 These technologies are available on instruments worldwide.

Iris Diagnostics-Beckman Coulter, Inc. (Brea, CA) was the pioneer in urine microscopic instrumentation, introducing the Yellow Iris in the 1980s; its most recent instrument is the Iris iQ200 microscopy analyzer. This analyzer is based on digital flow morphology (also called flowcell digital imaging) followed by urine particle recognition using proprietary neural network software. The iQ200 uses patented technologies to capture and automatically classify digital images of urine particles as they pass through a flowcell.

Urine microscopy analyzers of the second type use flow cytometry to identify and categorize the particles in urine. The UF-5000 analyzer is the latest version manufactured by Sysmex Corporation (Mundelein, IL), whereas the AUTION HYBRID is manufactured by Arkray, Inc. (Kyoto, Japan). In these flow cytometers, urine particles are identified and categorized based on forward scatter, fluorescence, and adaptive cluster analysis.2,3

The third technology used to perform automated urine microscopic analysis is automated digital microscopy that scans for urine particles on the single focal plane of a cuvette or cell. These analyzers take digital images of entire microscopic fields of view (FOVs) of urine components. The UriSed 2 analyzer manufactured by 77 Elektronika (Budapest, Hungary) uses proprietary software that identifies and classifies the urine sediment components. In contrast is the UD-10, a digital imaging device manufactured by Sysmex Corporation (Mundelein, IL) that is used solely combined with a Sysmex UF 5000 and requires an operator to assign particle classifications.

Digital Flow Morphology

The iQ200 Microscopy Analyzer can be purchased as a standalone instrument. It is an automated system that performs the microscopic examination of urine, as well as cell counts on body fluids (see Automation of Body Fluid Analysis section, later in this chapter).

Before the aspiration of 1 mL of urine, the analyzer mixes the sample. The aspirated urine is immediately sandwiched within a special fluid called lamina (iQ Lamina, Iris Diagnostics) that flows through a proprietary flowcell. The lamina and the flowcell are key to hydrodynamically orienting the particles in the urine. The flow path is at a specific depth of focus that enables precise microscopic viewing. The FOV of the microscope is coupled to a digital video camera, and stroboscopic illumination freezes the particles in motion as they stream past, which ensures blur-free imaging. With each sample, the camera captures 500 frames, digitizes them, and sends them to a computer for processing (Fig. 16.2). Note that the individual particles within each of the 500 frames are isolated as separate images, and the Auto-Particle Recognition (APR; Iris Diagnostics) software classifies each image (Fig. 16.3).

The APR software is a highly trained neural network that uses size, shape, contrast, and texture to automatically classify each image into one of 12 categories (Table 16.2). Next, the APR software calculates the concentration of each particle present. The results obtained for each sample are compared to user-defined auto-release criteria, and if the criteria are met, results can be sent to the LIS. If the criteria are not met, or if the option to auto-release reports to the LIS is not used by the laboratory, the results are stored and the user can review them at any time on the computer monitor.

Table 16.2

iQ200 Autoclassification and Subclassification Categories for Urine Sediment Particles

Blood Cells Crystals Casts Epithelial Cells Yeast Others
Autoclassified by analyser
Unclassified crystalsa

Budding yeast
Subclassified by user RBC clumps

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Oct 18, 2022 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Automation of Urine and Body Fluid Analysis

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