|How to cite this article:
Mohapatra S, Samantaray JC. Does naked eye examination of QBC capillary tube give a clue for malaria diagnosis?. Ann Trop Med Public Health 2013;6:263-4
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Mohapatra S, Samantaray JC. Does naked eye examination of QBC capillary tube give a clue for malaria diagnosis?. Ann Trop Med Public Health [serial online] 2013 [cited 2020 Oct 26];6:263-4. Available from: https://www.atmph.org/text.asp?2013/6/2/263/116515
Malaria is one of the commonest infectious diseases observed worldwide. Delay in the diagnosis leads to grave complications; hence, it presents a diagnostics challenge to many physicians. Microscopy using Giemsa stain is considered as reference standard for malaria diagnosis in endemic regions.  Reduced sensitivity, technical expertise, prolonged time for processing are some of the main drawbacks which make this test ill popular. This led to the development of more rapid and sensitive methods using fluorescence microscopy, e.g. Acridine Orange stain and Quantitative buffy coat assay (QBC). QBC assay is undoubtedly proven to be a highly sensitive, rapid, and reliable test detecting very low number of parasite.  In this paper, we are sharing some of our experience with QBC assay in this context.
In QBC assay, the capillary tube is coated with Acridine Orange (fluorescent dye,) which stains the nucleic acid (DNA as green color and RNA as orange color). A floater is inserted inside the capillary tube, which separates the white blood cells (WBC), red blood cells (RBC) and the parasites according to their densities. The WBCs are arranged in different layers forming visibly a discrete band above the RBCs layer called buffy coat. During the microscopic examination, parasites appear within the granulocytes and mononuclear cell layer. Some of the authors have commented on grayish black coloration of buffy coat predicting malaria positivity. , The normal color of buffy coat layer is whitish-to-buff [Figure 1]a. This layer appears black representing the malarial pigments within the parasites [Figure 1]b and this black color correlates with the degree of parasitemia. However, in sample containing more asexual forms (early trophozoites or late trophozoites without or less pigment, respectively), discoloration of this layer is either absent or faintly demarcated. When the tubes with blackish buffy coat layer are examined under low power objective of microscope, it appeared to contain black to brown dust like particles [Figure 2]. But, it was found to be clear in other tubes without discoloration. One of our samples was observed to have a black color ring above the buffy coat area [Figure 1]c. Careful microscopic observation of that area was found to be filled with malaria parasites. Hence we feel that a gross examination of QBC capillary tube around and the area above buffy coat layer can predict the malaria positivity as well as severity. Apart from buffy coat, high plasma color can signify certain medical conditions like jaundice. In adjunct to that, by looking at the packed cell volume in the tube, one can roughly give an estimate of hemoglobin level in the body. Gross examination of QBC capillary tube is a very useful method in detecting abnormality in terms of rapidity, easier identification and needs less expertise.
|Figure 1: Quantitative buffy coat capillary tubes showing the buffy coat layer (a) normal, (b) and (c) malaria positive|
|Figure 2: Microscopic observation of buffy coat layer under low power objective normal (a) malaria positive (b)
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Hence, we believe that, a careful macroscopic visualization of buffy coat discoloration will help an inexperienced laboratory personal to predict malaria positivity in addition to the status of anemia and jaundice. This observation may be utilized for further evaluation and therapeutic management of the patient in peripheral remote areas.
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Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]