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Year : 2019  |  Volume : 16  |  Issue : 1  |  Page : 46-50

Platelet count and indices in acute uncomplicated Malaria in Kano, Nigeria

1 Department of Heamatology, Bayero University Kano/Aminu Kano Teaching Hospital, Kano, Nigeria
2 Department of Medical Microbiology and Parasitology, Bayero University Kano, Kano, Nigeria
3 Department of Haematology and Blood Transfusion, Aminu Kano Teaching Hospital, Kano, Nigeria

Date of Web Publication5-Mar-2019

Correspondence Address:
Dr. Sharif Alhassan Abdullahi
Department of Microbiology and Parasitology, Bayero University, Kano
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/njbcs.njbcs_21_18

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Background: Quantitative and qualitative abnormalities of platelets are common among patients with malaria infection, and these correlate with severity. Few studies documented platelet changes in uncomplicated malaria in the endemic regions. This study aimed to describe the changes in platelet counts (PLTs) and automated platelet indices in uncomplicated malaria infection in a Nigerian population. Materials and Methods: This is a comparative cross-sectional study of 152 patients presenting with symptoms of uncomplicated malaria to the general outpatient Department of Aminu Kano Teaching Hospital, Kano, Nigeria. Malaria diagnosis was made using gold-standard microscopy of Giemsa-stained thick blood smear, while PLTs and indices (mean platelet volume [MPV], plateletcrit [PCT], platelet distribution width [PDW] and platelet-large cell ratio [P-LCR]) were determined using automated haematology analyser. Data were analysed using STATA v13 and results presented in descriptive terms. P =0.05 was considered statistically significant. Results: There were more female 8 (51.3%) than male 74 (48.7%) patients. A total of 84 patients (55.3%) were malaria positive. The prevalence of malaria-positive smears was higher in males 48 (31.6%) and among the age groups of 5–14 and 15–24 years (13.8% each). Thrombocytopenia was seen in 15 (19.7%) and 2 (2.6%) of malaria-positive and malaria-negative individuals, respectively, and the difference was statistically significant (P = 0.001). Platelet indices reveal significant differences in the MPV (P = 0.0016) and P-LCR (P = 0.0265) between malaria-positive and malaria-negative patients. Although both lower mean PLT and PCT, and higher PDW were found in malaria-positive than in malaria-negative individuals, this difference was not statistically significant (P > 0.05). Conclusion: This study showed that abnormalities in PLT and indices are more common among patients with an acute febrile illness who are malaria positive than those who are malaria negative.

Keywords: Kano, malaria, Nigeria, platelet indices, thrombocytopenia

How to cite this article:
Yusuf AA, Abdullahi SA, Idris IM, Jobbi YD. Platelet count and indices in acute uncomplicated Malaria in Kano, Nigeria. Niger J Basic Clin Sci 2019;16:46-50

How to cite this URL:
Yusuf AA, Abdullahi SA, Idris IM, Jobbi YD. Platelet count and indices in acute uncomplicated Malaria in Kano, Nigeria. Niger J Basic Clin Sci [serial online] 2019 [cited 2020 Jul 7];16:46-50. Available from: http://www.njbcs.net/text.asp?2019/16/1/46/253404

  Introduction Top

Infection by malarial parasites in humans has been associated with both qualitative and quantitative abnormalities of platelets. Several studies have documented thrombocytopenia as the most common platelet abnormality seen in malaria occurring in over 80% of patients, and in many, this may be severe.[1],[2],[3] Some studies have also identified thrombocytopenia as predictive for a poor prognosis for disease outcome in children with malaria.[4],[5] The exact mechanism of thrombocytopenia in this setting is not clear, but several factors have been suggested including decreased platelet lifespan from splenic sequestration, immune-mediated destruction and disseminated intravascular coagulation among others.[6],[7],[8] In spite of the frequent finding of thrombocytopenia in malaria, bleeding is not a frequent manifestation possibly as a result of the subsequent production of large and metabolically active, and hence haemostatically more competent, platelets from the bone marrow following peripheral destruction.[6]

Significant ultra-structural changes have also been found in platelets of patients with malaria, and the extent of abnormal findings correlated with the level of parasitaemia.[9] Early studies have demonstrated abnormally large platelets may be present in association with malarial infection, and that human platelets have been found to contain the malarial parasites.[10],[11] More recently, some platelet indices (MPV, PCT and PDW) have been evaluated in the setting of P. vivax infection in a Brazilian population.[12] These indices were found to exhibit significant variability with the potential to indicate disease severity.[12] Most studies conducted in non-endemic areas focused on the predictive value of thrombocytopenia in travellers returning from endemic areas.[13],[14] Within endemic areas, studies dwelt mainly on the value of thrombocytopenia as a marker of severity of malaria.[15] There are limited data on platelet changes in acute uncomplicated malaria in the endemic regions. Furthermore, the previous studies in our environment mainly used manual methods for platelet counts (PLTs) and blood film morphology, with higher error rates and subjectivity. The advent of automated blood analysers has made available certain parameters, the platelet indices, namely MPV, PCT, PDW and Platelet-Large Cell Ratio, (P-LCR) that are informative, more accurate and reproducible.

The aim of this study is, therefore, to describe the changes in PLTs and automated platelet indices in uncomplicated malarial infection in a Nigerian population.

  Materials and Methods Top

This is a comparative cross-sectional study that consecutively recruited 152 subjects over a period of 4 months (July 2017–October 2017). Individuals comprised both male and female patients under the age of 65 years who presented to the General Outpatient Department of Aminu Kano Teaching Hospital (AKTH) with an acute febrile illness suspected clinically to be acute uncomplicated malaria. Uncomplicated malaria is defined here clinically as presented with a history of fever (temperature ≥ 37.5°C) with no other obvious cause and no clinical or laboratory signs of severity or vital organ dysfunction (e.g., hyperpyrexia, impaired consciousness, severe anaemia and prostration).[16] Pregnant women, patients known to have HIV infection or other immunosuppressive illnesses and those on prophylactic antimalarial therapy at the time of presentation were excluded from the study. Informed consent was obtained from each participant before enrolment into the study and assent was also obtained for children under 18 years of age. Ethical approval was obtained from the Research Ethics Committee of the AKTH, Kano Nigeria.

The diagnosis of malaria was made through microscopic examination of Giemsa-stained thick blood smear performed by a trained microscopist who is a qualified medical laboratory scientist, and samples were treated as research samples. Detection of any levels of asexual forms of malarial parasites on thick blood smears was considered malaria-positive, and no further grading of parasitaemia or species determination was pursued in this study. PLTs and indices were determined from automated haematology analyser (Swelab alfa®, Boule Medical Diagnostics, Sweden) using ethylenediaminetetraacetic acid-anticoagulated venous blood. To avoid artifactual thrombocytopenia, all samples with visible clots on visual inspection of specimen bottle were rejected in accordance with the sample acceptance protocol at the AKTH haematology laboratory. Furthermore, samples with evidence of platelet clumping on microscopic examination of Romanowsky-stained thin blood film were also excluded for further platelet analyses. All samples were analysed within 2 h of collection during which period the samples were kept at room temperature. Thrombocytopenia was defined as PLT <115 × 109/L, being the lower reference limit for Africans[17] while reference ranges for platelet indices were taken to be 7.0–10.5 fL, 11%–18%, 0.15%–0.50% and 11.9%–66.9% for MPV, PDW, PCT and P-LCR, respectively.[18],[19] Data collected were entered into Microsoft Excel spreadsheet and analysed using STATA v13 (College Station, TX, USA). Results of continuous variables were compared between cases and controls using Student's t- test while those of categorical variables were compared using Chi-square test. P < 0.05 was considered statistically significant.

  Results Top

[Table 1] shows an overall distribution of the individuals based on age, gender and prevalence of malaria infection among them. There were 78 female (51.3%) and 74 male (48.7%) individuals in the studied population. Eighty-four individuals (55.3%) were malaria-positive, out of which male patients were found to have a higher prevalence of malaria 48 (31.5%) than the female individuals 36 (23.8%).
Table 1: Distribution of subjects based on age, gender and malaria positivity

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[Table 2] shows mean and standard deviation of PLT and indices for all patients with and without malaria infection. PLT was found to be lower among the individuals with malaria-positive smear (216.40 ± 122.82 × 109/L) than those with malaria-negative smear (244.46 ± 87.99 × 109/L). However, this difference did not reach statistical significance using the Student's paired t- test (P = 0.1078). Thrombocytopenia was seen in 15 (19.7%) among malaria-positive patients, while only 2 (2.6%) showed thrombocytopenia among those who are malaria-negative on blood smears. This difference was found to be statistically significant using Pearson Chi-square test (P = 0.001).
Table 2: Mean±standard deviation of the platelet indices for the subjects

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The MPV was observed to be slightly higher in malaria-positive patients (8.50 ± 0.08 fl) than those with malaria-negative (8.07 ± 0.11 fl) with a statistically significant difference between the two groups (P = 0.0016). PDW was also observed to be slightly higher among those subjects who are malaria-positive (12.01% ± 0.13%) than those who are malaria-negative (11.72% ± 0.15%), although this difference was not statistically significant (P = 0.1481). PCT was also observed to be slightly higher among malaria-negative (0.20% ± 0.01%) individuals than malaria-positive ones (0.17 ± 0.01%), and there was no significant difference between the groups (P = 0.0504). P-LCR was found to be higher (18.62% ± 0.58%) among malaria-positive patients than among malaria-negative individuals (16.63% ± 0.67%) with a statistically significant difference between the two (P = 0.0265).

  Discussion Top

This study demonstrated a higher prevalence of thrombocytopenia in malaria-positive than in malaria-negative patients. This is consistent with findings of previous studies.[1],[2],[3],[4],[5] The prevalence of thrombocytopenia found in among patients with uncomplicated acute malaria infection in this study is similar to 13.75% reported from Port-Harcourt, South-southern Nigeria.[20] However, it is lower than 59.7% from another report from Lagos[21] South-western Nigeria, but higher than 5.0% reported in children from Uyo,[22] South-southern Nigeria. The likely reasons for this wide disparity in the prevalence of thrombocytopenia in malaria in an endemic area are likely the differences in the techniques used for PLTs and the use of different cut-off values for thrombocytopenia by the different authors. For example, while the present study used automated cell counting and 115 × 109/L cut-off for thrombocytopenia, the study from Uyo[22] used 100 × 109/L as cut-off, while the one from Lagos[21] used both 150 × 109/L cut-off and manual method for blood cell counts.

Mechanisms leading to thrombocytopenia in malaria have been well established in the literature. Its prognostic significance and the link with poor outcome have also been recognised. Increasing evidence also suggest that platelets play a protective role in the host during erythrocytic infection by malarial parasites.[23],[24],[25] This protection has now been shown to be part of innate immunity and is mediated by platelet factor 4.[23],[26] A prospective study from Mangalore, India, reported by Faseela et al.,[27] found thrombocytopenia to have a sensitivity of 83% and a specificity of 68% in predicting malarial infection in patients with brief febrile illness in a malaria endemic region. The mean PLT in this study was also found to be numerically lower in malaria-positive patients than malaria-negative ones, even though this difference did not reach statistical significance. Lower PLTs is an expected finding given the known mechanisms of platelet destruction in malaria.

The advent of automated blood cell counting technologies has led to the generation of platelet indices that have proved to be useful in predicting the potential mechanism(s) of thrombocytopenia in the clinical setting. PCT, akin to haematocrit in red blood cells, is a platelet index that reflects overall platelet biomass. In this study, the mean PCT was higher in malaria-negative than in malaria-positive group, although this difference was not statistically significant. Typically, PCT parallels PLT as seen in this study, although it is a function of both PLT and MPV.[12]

MPV and PDW are measures of the average size and variation in sizes in the platelets respectively. In this study, MPV was found to be statistically higher among patients with smear-positive malaria than those with smear-negative, signifying the presence of larger platelets in patients with malaria. This is an expected finding in malaria where low PLT is mainly due to splenic sequestration or immune-mediated causes[7] leading to the release of young, hence larger platelets from the bone marrow. PDW, a measure of platelet anisocytosis, was also higher in malaria-positive than in malaria-negative individuals in this study, although the difference was not statistically significant. Higher PDW is equally expected in malaria since the excess destruction of platelets would trigger compensatory production of larger platelets, leading to the presence of platelets of varying sizes in the peripheral circulation, hence a high PDW. In normal individuals, MPV has been found to be inversely correlated with PLTs when measured by the impedance technology.[18] Studies have demonstrated distinct patterns of alteration in platelet indices in thrombocytopenic patients that are predictive of hypoproductive or hyperdestructive aetiologies.[28] In thrombocytopenias caused by peripheral destruction of platelets such as due to malaria, the MPV is generally higher than in conditions associated with decreased production such as in megaloblastic anaemia or aplastic anaemia due to the production of younger, hence larger platelets from the bone marrow in the former conditions.[18]

P-LCR, the proportion of platelets that have MPV above the upper limit of normal (12 fl), is indicative of the presence of megathrombocytes in circulation.[18] In this study, P-LCR was significantly higher among malaria-positive than malaria-negative patients. This is also an expected finding in malaria as the proportion of large platelets in circulation commonly increases following peripheral destruction leading to a higher P-LCR. P-LCR has also found utility in the differential diagnosis of abnormal PLTs being high in hyperdestructive and low in hypoproductive thrombocytopenia.[28],[29] More recently, altered platelet indices and their various ratios have also been found to predict mortality in hospitalised children.[30] In malaria infection, elevated MPV and PDW have been shown to correlate with high parasite density and warning signs of evolution to severe and complicated disease.[12] Important limitations in this study also need to be highlighted. We did not correlate PLTs or indices with the level of parasitaemia or species of parasites because grading of parasitaemia and species determination for malarial parasites were not pursued in this research. Future studies need to be designed to include both grading of parasitaemia and speciation to determine whether these parameters would influence the PLTs or the indices in malaria-infected patients. As this study was basically cross-sectional by design, correlation of the PLTs or indices with outcome of malaria infection was also not feasible. Statistical difference in all the studied indices might also be detected if a larger sample size than employed by the current study is used.

  Conclusion Top

This study demonstrated both lower mean PLTs and higher prevalence of thrombocytopenia among patients with acute uncomplicated malarial infection than patients without malaria in an endemic area. The study also showed that abnormalities of platelet indices are more common in malaria-positive patients compared to malaria-negative individuals. These findings are further validation of findings of previous studies.

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  References Top

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