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During the past century leucocyte differentiation was carried out on stained slides with a Romanowsky dye to highlight the different leukocyte properties of nucleic acids, acid mucopolysaccharides and proteins. There were many mechanical problems in smear preparation, including staining variability and the random distribution of cells on each slide1. The drop of blood on a slide was distributed by a spreader slide and the technologist would count 100 leukocytes to report respective values. Such enumerations on a very limited number of cells were inaccurate and non-reproducible2. Nevertheless, such results have been important guides for clinicians in patient care.
The introduction of machines to count blood cells was a progressive innovation. Rather than counts made on approximate volumes, a precise amount of blood was used. Currently auto-analyzers work to a calibrated blood volume, calculating percentages and absolute values per ΜL of blood. For example, the Coulter 5-diff analyzers (Beckman; Brea, CA, USA) aspirate 53 μL volumes with 25 μL processed to lyse red cells whole preserving the shape of the leukocytes. Leukocyte differentiation is based on differential light absorption3. Different generations of automated analyzers are available for a precise quantification of leukocytes in peripheral blood, and blood centers depend on their processes for the quality control of differing blood components4.
In resource-poor healthcare centers, financial restraints may prohibit use of the latest generation analyzers. Limited funds might may only allow purchase of basic models; however, even in such circumstances the aim of hematological investigators should always to acquire precise quantitative and qualitative knowledge of leukocyte, erythrocyte and platelet characteristics.
A reasonable compromise is in purchasing three- rather than five-diff analyzers, which are approximately one-quarter the cost of five-diff analyzers. Three-diff analyzers enumerate neutrophils and lymphocytes precisely and give pooled values for monocytes and eosinophils. With any three-diff analyzer, patients with non-polymorph, non-lymphocyte counts of ≥0.5 x 109 cells/L will require a peripheral blood smear examination, and this would address the profile of patients with visceral leishmaniasis, malaria and hematological monocytosis with >0.95 x 109 cells/L. Furthermore, cases of invasive helminthes infections, bronchial asthma and cutaneous allergy show eosinophilia with counts of ≥0.4 x 10109 cells/L. For example, for travelers returning to Israel from countries endemic for parasitic diseases, eosinophilia screening was executed with a cut-off value of ≥500 cells/μL5.
Therefore, clinicians in resource-poor or remote-health centers can provide better clinical care using less sophisticated analyzers, knowing the performance of the three-diff analyzers practically equals that of five-diff analyzers6.
Subhash C Arya, PhD
Nirmala Agarwal, FRCOG
Sant Parmanand Hospital, Delhi, India
References
1. Simmons A, Elbert G. Hemalog-D and manual differential leukocyte counts. American Journal of Clinical Pathology 1975; 64: 512-517.
2. Bauer JD. Numerical evaluation of formed elements of blood. In: AC Sonnenwirth, L Jarett (Eds). Gradwohl's clinical laboratory methods and diagnosis. St. Louis: CV Mosby, 1980; 800.
3. ACV Technology. In: Coulter RAC. TTM 5 diff Autoloader Hematology Analyzer. Instructions for use. Fullerton: Beckman Coulter, 2003; 2-3.
4. van der Meer PF, Dijkstra-Tiekstra MJ, Mahon A, de Wildt-Eggen J. Counting platelets in platelet concentrates on hematology analyzers: a multicenter comparative study. Transfusion 2008; 49(1): 81-90.
5. Meltzer E, Percik R, Shatzkes J, Sidi Y, Schwartz E. Eosinophilia among returning travelers: a practical approach. American Journal of Tropical Medicine and Hygiene 2008; 78(5): 702-709.
6. Arya SC, Agarwal N. Evaluation of automated blood count analyzers for utility in resource poor laboratories. Clinica Chimica Acta 2009 401(1-2): 187.