Clinical Chemistry I: Introduction to Beckman DXC Analyzers

Overview of the Beckman DXC 800

  • The Beckman DXC 800 is a console computer-controlled analyzer.

  • It is utilized for analyzing various sample types including:

    • Serum

    • Plasma

    • Urine

    • Cerebrospinal fluid (CSF)

    • Pre-treated whole blood

  • The analyzer performs general tests, therapeutic drug monitoring (TDM), and other tests.

  • Modular Chemistry (MC) analytes analyzed by the DXC 800 include:

    • Sodium

    • Potassium

    • Chloride

    • Total carbon dioxide

    • Calcium

    • Phosphate

    • Glucose

    • Urea

    • Creatinine

    • Total Protein

    • Albumin

    • Uric acid

  • The typical analysis time for tests is approximately 1 minute.

Main Components of the DXC

Analyzer Components:

  • Sample Handling

  • Modular Chemistry (MC)

  • Cartridge Chemistry (CC)

  • Hydropneumatic System

  • System Console

  • Water Supply

  • Waste Disposal

Sample Handling Procedures

Loading Samples:

  • Samples are loaded using sample racks or an autoloader tray.

  • Control buttons include:

    • RUN

    • Priority Load

    • STOP

  • The sample handling system includes:

    • Pushers

    • Gates

    • Shuttles

    • Barcode Reader

Analysis of Samples:

  • Samples are analyzed using:

    • Sample carousel

    • Sample probes for Modular Chemistry (MC) and Cartridge Chemistry (CC)

Storage of Completed Samples:

  • Completed samples are stored in an off-load tray.

Modular Chemistries

Reagent Storage:

  • Various reagent components stored for analysis including:

    • Electrolyte Injection Cup (EIC)

    • Flow cell assembly

    • Alkaline buffer reagent for CO2 measurement.

Reaction Mechanisms:

  • Modular chemistries utilize discrete reaction cup modules for the following components:

    • Urea

    • Phosphorous

    • Glucose

    • Creatinine

    • Total protein

    • Albumin

Hydropneumatics System

  • Provides:

    • Vacuum

    • Compressed air

    • Diluted wash solution

    • Deionized water

  • Caution: static-sensitive area.

Computer and Console

System Console:

  • Includes:

    • Monitor (touchscreen)

    • Keyboard

    • Mouse

    • Printer

Monitoring System:

Monitored Areas Include:

  • Temperatures

  • Power status

  • Hydro systems

  • Diagnostics on components

Analytical Principles of DXC

Ion-Sensitive Electrodes (ISE):

  • Measured ions include:

    • Na

    • K

    • Cl

    • CO2

    • Ca

  • The concentration of the ion is calculated from the difference in potential between a reference electrode and the measuring electrode.

Flow Cell Composition:

  • The flow cell is constructed from an acrylic block that houses the electrodes used for ISE measurements.

  • Specific ion-sensitive membranes include:

    • Sodium: aluminum silicate glass

    • Potassium: valinomycin

    • Chloride: Ag/AgCl

    • Calcium: ionophore membrane

    • CO2: measures pH rate changes.

ISE Reference:

  • Ensures a consistent measuring environment by using known concentrations of analytes to keep electrodes stable.

  • A reference reading is taken after each sample and subtracted from the buffer/sample dilution reading to assess variations in potential.

Buffer Solutions

ISE Buffer:

  • Used for patient sample dilution to prevent significant pH fluctuations.

  • It contains known concentrations of analytes to maintain consistency.

Advantages of Indirect Measurement Include:

  • Less sample volume required

  • Quicker analysis times

  • Reduced interference from sample components

Analytical Techniques for Specific Analytes

  • Urea: Urease reagent and conductivity increase measured with a gold conductivity electrode.

  • Creatinine: Measured using a colorimetric method (Jaffe reaction with alkaline picrate).

  • Glucose: Measured through the rate of oxygen consumption in a glucose oxidase reaction using a polarographic electrode.

  • Phosphorous: Colorimetric analysis with ammonium molybdate reagent.

  • Total Protein: Colorimetric method utilizing the Biuret reaction.

  • Albumin: Colorimetric measurement by dye binding with BCP.

Instrument Maintenance

Essential Routine Maintenance Schedule:

  • Daily, Monthly, Bi-monthly, 6-month, and Yearly checks are required to maintain efficient operation.

  • It's noted that 90% of problems happen after maintenance; however, caution is encouraged.

Daily Maintenance Tasks:

  • Check for any error codes on the screen.

  • Verify reagent levels and load appropriately.

  • Prime reagents and inspect for leaks.

  • Check calibration status and recalibrate if necessary.

  • Run quality control (QC) measures and clear the sample program after QC completion.

Monthly Maintenance Tasks:

  • Replace the cuvette wiper.

  • Clean the exterior of probes.

  • Clean the flow cell and modular chemistry cups.

  • Perform cleaning on cartridge chemistry probes.

  • Check calibration spans for chloride measurements.

Calibration Procedures

Calibration Timing Guidelines:

  • Required when:

    • Recommended by the manufacturer or upon calibration expiration

    • Quality control (QC) results indicate out-of-control status based on Westgard rules

    • New bottle/lots of reagent are loaded

    • After maintenance or repairs

    • New lot calibrator diskette is used

    • After rebooting.

Use of Calibrators:

  • AquaCal Calibrators Levels 1, 2, 3:

    • Used for analytes including Na, K, Cl, CO2, glucose, urea, creatinine, calcium, phosphate

    • Long-term storage occurs in a refrigerator; in-use bottles are kept at room temperature.

    • Calibration is daily for Na, K, Cl, CO2, calcium, and every 48 hours for glucose, urea, creatinine, and phosphate.

    • Protein calibrators are required monthly for total protein and albumin (TPm and ALBm).

Calibration Methodology:

  • Generally, 2 or 3 levels of calibrators are utilized for multiple chemistries, which are run in quadruplicate, discarding the highest and lowest readings, and using the middle values to establish a new calibration curve.

  • ADC (analog to digital conversion) process is employed for electrode potentials and absorbance measurements.

  • Accuracy, precision, and sensitivity checks are performed prior to finalizing the calibration curve.

Calibration Failure Analysis

Identifying Failure Parameters:

  • Possible failures in calibration might include:

    • Range (accuracy) issues caused by calibrator switching or malfunctioning instruments

    • Back-to-back (precision) errors which might arise from bubbles in the reagent lines

    • Span (sensitivity) problems from incorrect, contaminated, or improperly stored calibration reagents.

Systems Approach to Calibration Failure:

  • Consideration should include:

    • Sample-related factors (e.g., volume, hemolysis)

    • Reagent integrity and preparation protocols

    • Instrument calibration and maintenance history.

Quality Control Procedures

Running QC:

  • At least one set of quality controls with a minimum of two levels should be run per shift.

  • QC must be run following any calibration and upon suspected analytical issues.

  • Sample results must not be processed until QC has been verified as acceptable.

Troubleshooting QC Issues:

  • Common factors leading to QC failure include improper temperature storage of control vials.

Safety Precautions

  • Always ensure that power connections are grounded before operating any analyzer components.

  • Avoid contact near moving parts during operation.

  • Adhere to laboratory safety protocols regarding infectious or pathogenic material handling.

References

  • Beckman Coulter Instructions For Use: UniCel® DXC Synchron Clinical Systems. Volume 1. 2008

  • Beckman Coulter In-Lab Training Manual: UniCel® DXC 800. 2005

  • Clinical Chemistry: Principles, Techniques, and Correlations. 8th Edition by Bishop, M.L.; Fody, E.P.; Schoeff, L.E., Wolters Kluwer, 2018

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