The absolute recommendation of chamber Neubauer method for platelets counting instead of indirect methods in severe thrombocytopenic patients

A absoluta recomendação de se usar o método direto de contagem de plaquetas em câmara de Neubauer em pacientes intensamente plaquetopênicos

COMUNICAÇÃO BREVE SHORT COMMUNICATION

The absolute recommendation of chamber Neubauer method for platelets counting instead of indirect methods in severe thrombocytopenic patients

A absoluta recomendação de se usar o método direto de contagem de plaquetas em câmara de Neubauer em pacientes intensamente plaquetopênicos

Raimundo Antônio Gomes Oliveira^I; Maria Mariko Takadachi^II; Kimiyo Nonoyama^III; Orlando Cesar de Oliveira Barretto^IV

^IM.S.; assistant professor of Hematologia Clínica of Universidade Federal do Maranhão (UFMA); biochemist- pharmacist of the Hospital Universitário Presidente Dutra of UFMA, São Luís, MA, Brazil

^IIBiochemist-pharmacist, Laboratório de Hematologia of the Hospital dos Servidores Públicos do Estado de São Paulo, São Paulo, SP, Brazil

^IIIM.S., Seção de Hematologia of Divisão de Patologia of Instituto Adolfo Lutz, São Paulo, SP, Brazil

^IVM.D.; associate professor, Faculdade de Medicina of Universidade de São Paulo, LIM-23, São Paulo, SP, Brazil

^{Correspondence}

ABSTRACT

Accurate and precise platelet counting is crucial for recommending platelets transfusion for thrombocytopenic patients, principally when platelet counts are bellow 30,000/µl. As most laboratories still use the indirect methods for confirming low automated platelet counts, this work compared two indirect methods used in practice (Fonio and Nosanchunk et al.) with the International Committee for Standardization in Hematology recommended direct method (Brecher and Cronkite). The obtained data show that the indirect methods present low precision and accuracy, and that the direct method should always be employed in severe thrombocytopenic samples thanks to its high precision.

Keywords: platelet counts, thrombocytopenia, quality control, platelet transfusion

RESUMO

A contagem precisa e exata de plaquetas é crucial para se indicar ou não a transfusão de plaquetas em pacientes plaquetopênicos, principalmente quando as contagens estão abaixo de 30.000/µl. Como muitos laboratórios ainda utilizam as contagens indiretas em esfregaço para confirmar baixas contagens obtidas por automação, este trabalho se propôs a comparar dois métodos indiretos muito usados (Fonio e Nosanchunk et al.) com o método direto indicado pelo Comitê Internacional de Estandardização em Hematologia (ICSH) (Brecher e Cronkite). Os dados obtidos demonstram que os métodos indiretos em esfregaço apresentam baixa precisão e exatidão e que o método direto de referência deve ser usado para confirmar as contagens em amostras intensamente plaquetopênicas.

Unitermos: contagem de plaquetas, plaquetopenia, controle de qualidade, transfusão de plaquetas

Introduction

Platelet counting is an important tool used in clinical investigation to avoid bleeding risks. There is a general agreement that automation brought precision and accuracy for platelet counts in healthy individuals. Nevertheless, reliable platelet counts in thrombocytopenic patients is still controversial (6, 11, 15, 19).

Based on the studies of Gaydos et al. (1962), most of the institutions use 20.000/µl (7) as threshold for platelet transfusion, whereas others employ 10.000/µl (3, 9, 10, 14, 16, 17).

The Brecher and Cronkite (4, 5) direct manual method has been recommended by the International Committee for Standardization in Hematology ICSH (1984/1988).

Unfortunately the majority of hematology laboratories still employ indirect manual methods (blood smears) for confirming low platelet counting obtained in automated counters. The objective of this work was to evaluate the most used indirect methods and compare them with the manual direct standard method.

Methods

Peripheral blood samples of 43 thrombocytopenic patients with platelet counts lower than 30,000plt/µl were analyzed. They were collected at the Hematology Service of the Hospital do Servidor Público Estadual (São Paulo-SP).

Blood smear indirect method 1: Nosanchung et al. (18) and Apibal et al. (1). Blood smear indirect method 2: Fonio (8).

ICSH (1984/1988) (12, 13) direct reference method: the Brecher and Cronkite method (4, 5), which requires Neubauer improved counting chamber.

The indirect platelet counting methods were performed in triplicate. Each count was obtained as the mean of 10 oil immersion fields (1000x amplification), in a total of 30 fields.

The ICSH method was also analyzed by triplicate counts. For every counting a sample was diluted in triplicate. The minimum of 200 platelets at Neubauer chamber was taken as standard procedure. The mean, standard deviation, and coefficient of variation for the manual (direct and indirect) platelet counts were compared with the direct method. Analysis of variance statistical test was employed.

Results

The results are shown in Tables 1 and 2. They indicate that indirect manual methods with variation coefficients higher than the upper acceptable threshold (15%) have lower precision and accuracy when compared to the direct reference method (Tables 1 and 2).

Discussion

According to Berkson (2), the specific error of hemocytometer depends on the number of cells which are counted in each area of the reticulum. Using the formula proposed by this author in similar conditions to this study, the chamber error itself would be of CV = 7.59%. Therefore, as 200 cells were always counted, these experiments disclosed CV = 10.49% for platelet counts less than 30,000/µl, and are similar to the data obtained by Dickerhof et al. (6) for platelets around 10,000/µl (CV = 14.7%). Hanseler et al. (11) results show that the correct use of the Neubauer chamber presents a satisfactory precision (CV < 15%) in counts above 4,000plt/µl.

The results listed in Tables 1 and 2 indicate that the direct hemocytometer method is much more precise than the indirect methods in thrombocytopenic patients. For levels lower than 40,000plt/µl, the results obtained by Lawrence (16) (CV = 30.4%, p < 0.001) confirm the lower precision of indirect methods.

Based on the threshold established for prophylactic platelet transfusion (10,000 or 20,000plt/µl), the results obtained by the indirect methods show that even triplicate counts, of 10 fields each, may jeopardize the clinical decisions when prophylactic or even therapeutic platelet transfusion are in discussion.

Conclusion

The direct Neubauer chamber method for levels lower than 30,000plt/µl seems to be the most accurate and precise method for patients presenting bleeding risks.

When precision is required for taking decisions regarding platelet transfusion indication, the blood smear methods are not helpful and may even impair them.

Recebido em 19/03/02

Aceito para publicação em 12/12/02

This work is part of Raimundo Antônio Gomes Oliveira's mastership thesis presented to the Faculdade de Ciências Farmacêuticas of USP in June, 2000

• 1. Apibal, S. et al The effects of hemotocrit on visual platelet estimation. Am. J. Med. Technol., 45: 785-86, 1979.
• 2. Berkson, J. et al The error of estimate of blood cell counts as made with the hemocytometer. Am. J. Physiol., 128: 309-23, 1940.
• 3. Beutler, E. Platelet transfusions: the 20,000/µl trigger. Blood, 337: 1914-15, 1997.
• 4. Brecher, G. & Cronkite, E.P. Morphology and enumeration of human blood platelets. J. Appl. Physiol., 3: 365-77, 1950.
• 5. Brecher, G. et al The reproducibility and consistency of the platelet count. Am. J. Clin. Pathol., 23: 15-26, 1953.
• 6. Dickerhoff, R. et al Enumeration of platelets by multiparameter flow cytometry using platelet-specific antibodies and fluorescent reference particles. Clin. Lab. Haematol., 17: 163-72, 1995.
• 7. Finazzi, G. Prophylactic platelet transfusion in acute leukemia: which threshold should be used? Haematologica, 83: 961-62, 1998.
• 8. Fonio, A. Ueber ein neues Verfahren der Blutplattchenzahlung. Deustche Zeitschrieft Fur Chirurgie, 117: 176, 1912.
• 9. Gil-Fernandez, J.J. et al Clinical results of a stringent policy on prophylactic platelet transfusion: non-randomized comparative analysis in 190 bone marrow transplant patients from a single institution. Bone Marrow Transp., 18: 931-35, 1996.
• 10. Gmür, J. et al Safety of stringent prophylactic platelet transfusion policy for patients with acute leukemia. Lancet, 338: 1223-26, 1991.
• 11. Hanseler, E. et al Estimation of the lower limits of manual and automated platelet counting. Am. J. Clin. Pathol., 105(6): 782-87, 1996.
• 12. ICSH International Committee for Standardization in Haematology. Selected method for visual platelet counting. Labmedica, 5: 31-4, 1988.
• 13. International Committee for Standardization in Haematology. Protocol for evaluation of automated blood cell counters. Clin. Lab. Haematol., 6: 69-84, 1984.
• 14. Kruskall, M.S. The perils of platelet transfusions. New Engl. J. Med., 337: 1914-15, 1997.
• 15. Kunicka, J. et al Accurate quantitation of platelets on the Advia^™ 120 hematology system. In: Bayer. Advia^™ 120 Hematology System.
• 16. Lawrence, J.B. et al Reliability of automated platelet counts: comparison with manual method and utility for prediction of clinical bleeding. Am. J. Hematol., 48: 244-50, 1995.
• 17. Navarro, J.T. et al Prophylactic platelet transfusion threshold during therapy for adult acute myeloid leukemia: 10,000/µl versus 20,000/µl. Haematologica, 83: 998-1000, 1998.
• 18. Nosanchuk, J.S. et al The analytic basis for the use of platelet estimates from peripheral blood smears. Am. J. Clin. Pathol., 69: 383-85, 1978.
• 19. Stanworth, S.J. et al Automated counting of platelets on the Bayer Advia^™ 120 analyser. Clin. Lab. Haematol., 21: 113-7, 1999.

Publication Dates

• Publication in this collection
  17 July 2004
• Date of issue
  June 2003

History

• Received
  19 Mar 2002
• Accepted
  12 Dec 2002