Featured Article
Please see our Hematology Analyzers section to find manufacturers that sell these products
Hematology analyzers are used widely in patient and research settings to count and characterize blood cells for disease detection and monitoring. Basic analyzers return a complete blood count (CBC) with a three-part differential white blood cell (WBC) count. Sophisticated analyzers measure cell morphology and can detect small cell populations to diagnose rare blood conditions.
The three main physical technologies used in hematology analyzers are: electrical impedance, flow cytometry, and fluorescent flow cytometry. These are used in combination with chemical reagents that lyse or alter blood cells to extend the measurable parameters. For example, electrical impedance can differentiate red blood cells (RBCs), WBCs, and platelets by volume. Adding a nucleating agent that shrinks lymphocytes more than other WBCs makes it possible to differentiate lymphocytes by volume.
Electrical impedance
The traditional method for counting cells is electrical impedance, also known as the Coulter Principle. It is used in almost every hematology analyzer.
Whole blood is passed between two electrodes through an aperture so narrow that only one cell can pass through at a time. The impedance changes as a cell passes through. The change in impedance is proportional to cell volume, resulting in a cell count and measure of volume.
Impedance analysis returns CBCs and three-part WBC differentials (granulocytes, lymphocytes, and monocytes) but cannot distinguish between the similarly sized granular leukocytes: eosinophils, basophils, and neutrophils.
Counting rates of up to 10,000 cells per second can be achieved and a typical impedance analysis can be carried out in less than a minute.
Flow cytometry
Laser flow cytometry is more expensive than impedance analysis, due to the requirement for expensive reagents, but returns detailed information about the morphology of blood cells. It is an excellent method for determining five-part WBC differentials.
A single-cell stream passes through a laser beam. The absorbance is measured, and the scattered light is measured at multiple angles to determine the cell’s granularity, diameter, and inner complexity. These are the same cell morphology characteristics that can be determined manually from a slide.
Adding fluorescent reagents extends the use of flow cytometry to measure specific cell populations. Fluorescent dyes reveal the nucleus-plasma ratio of each stained cell. It is useful for the analysis of platelets, nucleated RBCs, and reticulocytes.
Proprietary technologies
Manufacturers combine these three technologies with innovative uses of reagents, hydrofluidics, and data analysis tools to produce proprietary methods, each of which has strengths in terms of accuracy, speed, or breadth of parameters.
Siemen’s (www.healthcare.siemens.com) ADVIA® instruments use peroxidase staining for differential testing. This provides a secondary total WBC that acts as an internal QC check.
The Sysmex (www.sysmex.com) sodium lauryl sulfate method for hemoglobin analysis is a noncyanide method with very short reaction times. Hemoglobin is determined in a separate channel, minimizing interference from high leukocyte concentrations.
The Abbott (www.abbottdiagnostics.com) CELL-DYN Sapphire® uses three-color fluorescence combined with patented MultiAngle Polarized Scatter Separation technology to deliver accurate WBC enumeration and identification using four angles of light scatter.
What to consider when buying a hematology analyzer
Your choice of instrument will be driven primarily by the setting of use: patient bedside, consulting room, clinical lab, or research lab. Note that instruments must have regulatory approval for clinical as opposed to research use.
Other considerations include:
- Range of tests
- Time per analysis
- Automation
- Reagent supply
- Sample size and microsampling
- Accuracy, precision, and linearity
- Maintenance, calibration, and QC
- Results analysis and storage
- Footprint.
Range of tests
Every hematology analyzer returns a CBC and a three- or five-part WBC differential. However, even the simplest analyzer will return multiple parameters. The most basic analyzer from Sysmex, the XP-300™, returns 17 parameters: WBC; RBC; HGB; HCT; MCV; MCH; MCHC; PLT; NEUT #,%; LYM #,%; MXD #,%; RDW-SD; RDW-CV; and MPV.
By contrast, the Pentra DX Nexus SPS evolution from Horiba (www.horiba.com) measures 50 parameters: WBC, RBC, HGB, HCT, MCV, MCH, MCHC, RDW, PLT, MPV, *PCT, *PDW %, NEU, LYM, MON, EOS, BAS, *ALY, *LIC, *IMM, *IML, *IMG: (% and #), RET (% and #), RETH %, RETM %, RETL %, *IMR %, CRC%, IRF, MRV, *RHCc, MFI, NRBC % NRBC#, *CWBC, *WBC#, *RBC#, *PolyNuc#, and *MonoNuc# (* parameters for research use only).
Consider whether there is a choice of tests to run, or whether every parameter is measured for every sample. Check the cost per run since extensive test menus will incur higher reagent costs.
Time per analysis
Time per analysis depends on the parameters being measured. The rate limiting step is the reaction time for reagents. A simple CBC can typically be returned in 1 min. More sophisticated analyses can take up to 10 min.
Abbott’s CELL-DYN Sapphire provides a reportable CD61 immunoplatelet count in approximately 5 min, and CD3/4 and CD3/8 immuno T-cell count in approximately 7 min.
Automation
High-throughput labs require automation of their hematology workflow and the capability to integrate with other systems. Factors to consider are throughput, autoloader capacity, and whether vials and racks are compatible with other lab equipment.
The Sysmex XE-5000 reports 31 whole blood parameters at a rate of 150 samples/hr.
The ADVIA 120 from Siemens is a benchtop instrument with a 150-capacity rack-based autosampler, allowing 75 min of walkaway operation.
Pentra DX Nexus SPS evolution from Horiba has an autoloader with continuous loading capability. The rack is compatible with most pre- and postanalytical systems.
If you require barcode tracking, check the quality of the imaging technology. Coulter LH 780 analyzers (Figure 1) from Beckman Coulter (www.beckmancoulter.com) are capable of reading most barcode labels, even those with lower print quality.
Many manufacturers offer integrated slide-making and staining modules that can be added on to the instrument.
Check the system’s capability for flagging outlying results. Automatic flagging and retesting minimize the requirement for manual review.
Figure 1 – The automated Coulter LH780 from Beckman Coulter identifies and enumerates NRBCs without manual intervention. Image courtesy of Beckman Coulter, Inc.Reagent supply
When choosing an instrument, check how many reagents are required and the costs and safety requirements. Can they be purchased from any supplier, or only the manufacturer?
Erba’s (www.erbalachema.com/en/) ELite 3 measures 20 parameters with only three reagents, which are environmentally friendly and cyanide free. Beckman Coulter’s DxH 800 and DxH 600 use only five reagents for all analyses, including NRBC and reticulocytes.
Ask how often the reagents need to be changed. The ADVIA 120 from Siemens carries enough onboard analytical and wash reagents for 1850 CBC/diff tests.
Sample size and microsampling
Typical sample size requirements are on the order of 150 μL of whole blood for multiparameter analysis. Many manufacturers offer microsampling, which is particularly helpful for pediatrics. The Horiba ABX Micros ES 60 uses 10 μL of whole blood for CBC plus WBC 3-diff.
Accuracy, precision, and linearity
Ask to see the manufacturer’s data on accuracy, precision, and linearity. The accuracy of volume measurements using impedance can be greater than 1% and depends on the width of the aperture relative to the cell being measured. Some instruments use multiple-sized apertures to improve accuracy for different-sized cells. Temperature also affects accuracy. The Horiba Pentra 80 features a preheated analysis chamber to ensure consistent results.
Calibration, maintenance, and QC
Consider how frequently the instrument must be cleaned and recalibrated. Ask what QC features are included.
Idexx (www.idexx.com) includes qualiBeads® in its analyzers. qualiBeads are particles with specific characteristics that are used as an internal standard to verify pipetting accuracy and laser performance.
The Horiba ABX Pentra manages reagent standardization, validation, and reruns and can also share rules between a central laboratory and satellite laboratories.
Open or closed tube sampling
Closed tube sampling reduces the risk of exposure to blood. Instruments with open or closed sampling options have different stability and calibration requirements depending on the mode of operation.
Table 1 – Hematology analyzer manufacturers
Results storage and analysis
A major differentiator between analyzers is the number of results that can be stored on the system. A small benchtop analyzer might typically save 1000 patient results with histograms. The Horiba ABX Pentra DX120 SPS will store 90,000 results plus graphics.
Many high-throughput machines will integrate with existing LIMS.
Footprint
Systems vary from small benchtop units to large automated machines. The ABX Micros ES 60 from Horiba is a compact benchtop unit that delivers CBC + 3–diff. It has a touchscreen interface and can store 1000 patient results with histograms. It has a footprint of 16.9 in. × 14.2 in. × 14.2 in. and weighs only 30.9 lb.
The freestanding automated XN-9000 from Sysmex is scaleable. The 801 model is 26 ft long × 4 ft deep and can analyze 120 slides/hr and 900 CBCs/hr. If linear floor space is limited, a corner unit can be added.
Consider the ergonomics of operation and the quality of the display screen.
Analyzers for veterinary use
Hematology analyzers are specific to the species of blood to be analyzed. A dedicated machine or add-on is needed to measure the different characteristics of animal species
For veterinary applications check the number of species. The ProCyte Dx analyzer from Idexx can process canine, feline, equine, bovine, ferret, rabbit, gerbil, pig, guinea pig, and mini pig samples.
Coulter Ac·T Veterinary Applications Software from Beckman Coulter covers cats, dogs, and horses.
Manufacturers
Table 1 lists a number of leading manufacturers of hematology analyzers.
Please see our Hematology Analyzers section to find manufacturers that sell these products
Katriona Scoffin, B.Sc., is a freelance science writer; e-mail: [email protected]