Automated hematology analyzers provide a fast, accurate way to perform important clinical tests, namely complete blood counts (CBC), and save laboratories the time and error risk of performing these counts manually. However, modern clinical hematology analyzers can also do much more, providing expanded menus of test parameters and leveraging advanced techniques like flow cytometry to increase the scope of what can be learned from a blood test. With many different options for hematology testing instruments on the market, it is important to know the differences between varying measurement technologies, specifications and features these systems may include. This guide provides a breakdown of key factors to consider when choosing a hematology analyzer for your lab.
3-Part vs. 5-Part Differential Analyzers
CBC screenings are one of the most frequent routine tests performed at clinical laboratories, and a typical automated hematology analyzer will allow for red blood cell (RBC), white blood cell (WBC), platelet (PLT) counts and hematocrit (HCT) calculation via electrical impedance methods, as well as hemoglobin (HGB) concentration via photometry or spectrophotometry. Typically, WBC differential results are also provided, but some analyzers enable only a three-part differential based on size (granulocytes, mid-sized WBCs, and lymphocytes) while others provide a five-part differential (neutrophils, basophils, monocytes, eosinophils and lymphocytes).1 The more precise five-part differential measurement is enabled through flow cytometry, while analyzers that use only impedance measurements without flow cytometry can only differentiate between the three size categories mentioned.
For many general laboratory applications, such as routine tests performed by a low-volume physician office laboratory, three-part differential tests are sufficient to aid in decisions such as whether to treat an infection with antibiotics.2 Three-part differential analyzers also have the benefits of being a fraction of the cost of analyzers that rely on flow spectrometry, requiring fewer reagents and having lower maintenance costs as well. However, more specialized labs, such as oncology and allergy labs, can benefit from the more detailed analysis provided by five-part differentiation. Additionally, due to their precision, five-part analyzers can significantly reduce the amount of samples that require manual differentiation, which could save substantial time and hassle, especially for higher-throughput labs.
Choosing between a 3-part analyzer or 5-part analyzer, or between an analyzer that uses flow cytometry versus one that doesn’t, will be one of the first steps in selecting an automated hematology system. Budget, testing volume and specific diagnostic or research application will all go into deciding which type is right for your lab. Also consider whether additional testing possibilities enabled by flow cytometry, such as reticulocyte count, could be beneficial, and whether fluorescence methods can be used to improve analysis.3
Accuracy and Precision
Both electrical impedance and flow cytometry methods provide high accuracy for CBC and differential measurements, but certain factors may provide improved accuracy and precision for greater first-pass efficiency and confidence in results. For example, many analyzers now use hydrodynamic focusing with electrical impedance to prevent recirculation and edge effects.4 This ensures cells are not caught behind the orifice and erroneously recounted, and that cells are always focused into the center of the aperture, providing consistent impedance profile. Accuracy can also be affected by the width of the aperture relative to the size of the cell being measured, and some instruments utilize multiple-sized apertures to further enhance accuracy.3 Maintaining a consistent temperature inside the analysis chamber can also yield more consistent results. Consider whether an instrument includes controls to allow for automatic monitoring, flagging and correction of temperature changes during runs.
Manufacturers should provide clear data on accuracy, precision and linearity for each major parameter measured by the system. First-pass efficiency is another important consideration, as fewer samples requiring additional analysis means more time savings and higher throughput.
Sample Throughput and Size
Both the volume of samples coming through your lab, and the physical volume of the blood samples collected, will play a key role in your requirements for a suitable hematology analysis system. Sample throughput is a critical specification to look at for any system you may be considering. On the low end, benchtop analyzers for low-volume laboratories may provide a throughput of around 30-50 samples per hour. For high volume labs, analyzers with a capacity of up to 100 samples or more per hour are available, along with scalable solutions to more effectively integrate multiple instruments and workflow steps for greater throughput and efficiency. As can be expected, greater throughput instruments generally come at a higher cost.
The sample size requirement of the instrument is another number to keep your eye on. A typical sample volume requirement may fall between 100-200 µL, but many more analyzers are now enabling analyses with lower sample volumes, down to microsampling requirements of just 10-20 µL. These lower requirements can be especially helpful for labs that may regularly process low-volume samples, such as pediatric doctor’s offices and hospitals. Testing modes beyond a basic CBC and three-part differential, such as a five-part differential or a CBC plus C-reactive protein (CRP) assay, often have greater sample volume requirement, but volumes around 20-30 µL are still possible on some systems.
Labs considering a microsampling system should be aware of some common issues that can come up when when using small capillary blood samples, which could lead to discrepancies between venous and capillary blood results; for example, platelets may adhere to the walls of capillary sampling tubes and form clumps, leading to lower PLT counts and falsely elevated lymphocyte counts.5 The prospective buyer should consider the differences in sample handling requirements for smaller samples and ensure they can verify that the instrument delivers consistent and accurate results for the required tests using small volumes of capillary blood.
Reagent System
The reagent requirements of a system may factor into a number of considerations such as reagent costs, safety, maintenance and environmental impact.3 Analyzers that can test a greater number of parameters may require a wider range of reagents. Some systems can measure well over a dozen reportable parameters using just two or three reagents, but this may also mean restriction to proprietary reagents from the same manufacturer, for which costs and refill frequency should be closely examined. Safety considerations are also an important factor - for example, non-cyanide methods for HGB measurements may be preferred over methods that require the use of cyanide. Questions prospective buyers should ask include:
- How many reagents are required for the parameters I want to test?
- How many tests can I run before the reagent must be replaced?
- Can reagents be purchased from any supplier, or only the manufacturer?
- Can non-toxic reagents be used?
- What are the waste disposal requirements for the reagents used by this instrument?
Hematology Analyzer Vendors to Consider
- Abbott
- Beckman Coulter
- Boule
- Horiba
- Mindray
- Siemens
- Sysmex
References
- "Go to the Next Level with 5-Part Differential Hematology Analyzers," Blog, Beckman Coulter (2021). https://www.beckmancoulter.com/en/blog/diagnostics/go-to-the-next-level-with-5-part-differential-hematology-analyzers
- "Hematology analyzers: 3-part or 5-part, that is the question," White Paper, Boule (2019). https://boule.com/content/uploads/2021/03/whitepaper-3p-or-5p-hematology-analyzers-31183-2.pdf
- "Hematology Analyzers—From Complete Blood Counts to Cell Morphology," Article by Katriona Scoffin, Labcompare (2014).
https://www.labcompare.com/10-Featured-Articles/162042-Hematology-Analyzers-From-Complete-Blood-Counts-to-Cell-Morphology/
- "Electrical Impedance Methodology," Hematology & Hemostasis Academy, Abbott. https://hematologyacademy.com/hematologymethod/electrical-impedance-methodology/
- "Sampling procedure for optimized performance with the capillary inlet," Knowledge Center, Boule. https://boule.com/knowledge-center/sampling-procedure-for-optimized-performance-with-the-capillary-inlet/