Standard white blood cell count for malaria density estimation: A need for review?

Abstract

To compare the actual white blood cell (WBC) counts, used to calculate malaria parasite densities against the standard WBC counts of 8000/µl. The WBC counts of 111 Plasmodium falciparum -infected children in north central Nigeria, Aged 1-4 (<5) and 5-14 (>5) years were estimated in a cross-sectional study. These gave average values of 7487/µl and 5985/µl against the assumed standard count of 8000/µl. A comparison of blood samples grouped into those with WBC counts of 8000/µl (3.95% and 8.57%), those below (57.89% and 82.86%) and above (38.16% and 8.57%) showed a significantly higher number in the group below the standard value for the two age groups (X2, df = 3, P > 0.05). This paper draws attention to the disparity between the assumed standard WBC counts and the real values encountered among Nigerian children and proposes a review for achieving more accurate malaria parasite density estimation among other reasons. To best of our knowledge, the present study is the first such report from north central Nigeria.

Keywords: Children, parasite density, review, standard, white blood cell count.

How to cite this article:
Omalu IC, Oguche S, Gyang V P, Akindigh T M, Egah D Z, Gokop B. Standard white blood cell count for malaria density estimation: A need for review?. Ann Trop Med Public Health 2008;1:29-30
How to cite this URL:
Omalu IC, Oguche S, Gyang V P, Akindigh T M, Egah D Z, Gokop B. Standard white blood cell count for malaria density estimation: A need for review?. Ann Trop Med Public Health [serial online] 2008 [cited 2013 Apr 20];1:29-30. Available from: https://www.atmph.org/text.asp?2008/1/1/29/43075
Introduction

White blood cells (WBCs) are one of the numbers of different cells that play a part in the body’s defenses and give immunity against disease. Their numbers may be reduced (leucopenia) by starvation, pernicious anemia, and certain infections, such as typhoid and malaria. An increase in their numbers (leucocytosis) is a reaction to normal events such as digestion, exertion, and pregnancy, and to abnormal ones such as loss of blood, cancer, and most infections. WBC counts during malaria are generally characterized as being low to normal, a phenomenon that is widely thought to reflect localization of leukocytes away from the peripheral circulation and to the spleen and other marginal pools, rather than actual depletion or stasis. Leukocytosis is typically reported in a fraction of cases and may be associated with concurrent infections and/or poor prognosis. [1] Remarkably, few published studies have compared actual and standard WBC counts in malarial parasite-infected people in endemic areas. Although several methods for estimation of densities of blood-stage parasites by microscopy are in use, the most common is to count the number of asexual parasites seen relative to a given count of WBCs (usually 200 or 500 cells) and then to multiply the parasite: WBC ratio by 8000, the assumed number of WBCs per microliter of blood. This assumed standard value; most often does not give the true value instead, it under or overestimates it.

Materials and Methods

Patients were those who presented to Barkin Ladi General Hospital in Plateau state, Nigeria, during a drug study between February 23, 2007 and May 23, 2007 and had fever (oral temperature of >37.5°C), headache, or a self-reported history of fever within the previous 72 h. The oral temperatures of each patient were taken immediately before blood was obtained. Blood was tested immediately for malaria parasites using the giemsa staining technique and about 3 ml in tubes, were transported on ice within 2 h to a laboratory, and, within 6 h of the initial sample collection, WBCs were counted by a Coulter automated cell counter (Beckman-Coulter) in Jos, Nigeria and a QBC centrifugal hematology system (Becton-Dickinson Diagnostic Systems). Simple means, standard deviation, and chi-square were used in comparing WBCs indifferent age groups (<5 and ≥5 years old).

Results

[Table 1] shows the actual values of WBC counts against the standard values. For the two groups, the values is below the standard and it is significant using the Chi-square at 5%, though there are more WBC counts in children above the age of 5 years. [Table 2] gives the percentage distribution of WBCs for which a higher percentage of children from the two groups fall below the standard value. The difference in these values against the standard is also significant at 5%.

Discussion

Our analysis of WBC counts in individuals presenting at Barkin Ladi General Hospital in which all children tested positive for P. falciparum showed that most children fall below the standard value, which grossly overestimates the parasite density for such children. This can be compared to the work of Jeremiah et al . when they studied the comparative analysis of malaria parasite density using actual and assumed WBC counts, in which they showed that parasite density estimation using the assumed count of 8.0 × 10 9 /l might result in overestimation of the parasite burden. [2]

Previous study in India showed a discrepancy between the actual WBC counts and the standard with patients having as low as 4000//µl, which overestimated the parasite density, though they did not describe the methods used for determination of WBC. [3] Rzepczyk and Swan also got similar observations in their various studies. [4],[5]

It is important that the actual WBC counts are used especially when conducting drug therapeutic efficacy studies in other to get the true picture of the efficacy of malaria drugs.

Conclusion

The use of actual WBC counts is more appropriate than the assumed WBCs.

Acknowldgments

We thank the management of Barkin Ladi General Hospital and Jos University Teaching Hospital, for their dedication and technical assistance, and gratefully acknowledge the contributions Late Prof. N. B. Molta who started this study but could not finish it.

References
1. McKenzie FE, Prudhomme WA, Magill AJ, Forney JR, Permpanich B, Lucas C, et al. White blood cell counts and malaria. J Infect Dis 2005;192:323-30.
2. Jeremiah AZ, Uko EK. Comparative analysis of malaria parasite density using actual and assumed white blood cell counts. Ann Trop Paediatr 2007;27:75-9.
3. Jadhav UM, Singhvi R, Shah R. Prognostic implications of white cell differential count and white cell morphology in malaria. J Postgrad Med 2003;49:218-21.
4. Rzepczyk CM, Stamatiou S, Anderson K, Stowers A, Cheng Q, Saul A, et al. Experimental human Plasmodium falciparum infections: Longitudinal analysis of lympho-cyte responses with particular reference to gamma delta T cells. Scand J Immunol 1996;43:219-27.
5. Swan JM. A contribution to the question of the leucocyte formula in malaria. Am J Trop Med Hyg 1922;2:283-8.

DOI: 10.4103/1755-6783.43075

Tables

[Table 1], [Table 2]

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