Key words

Blood count, thrombocytosis, hyperleucocytosis, infection.


Thrombocytosis is a frequently abnormality of complete blood count. The role of the biologist is then very important to advise the clinician in the etiological approach, as well as to evaluate a possible thrombotic or haemorrhagic risk. In the majority of cases (90%), thrombocytosis is reactive, resulting from an underlying pathology (iron deficiency, inflammatory cause, etc.) [1]. In addition, non-secondary thrombocytosis, corresponds to a chronic myeloproliferative syndrome (essential thrombocythemia, primary polycythemia, primary myelofibrosis, chronic myeloid leukemia) [2]. Next to the etiological assessment, one of the challenges is to evaluate and manage a possible thrombotic or haemorrhagic risk. Knowing the factors associated with thrombocytosis will facilitate the management of patients to improve their life expectancy. Thus, this study aims to describe the factors associated with thrombocytosis in hospital patients and out patients.

Materials And Methods

We undertook a case-control study of thrombocytosis between December 01, 2017, and May 31, 2018 in the laboratory of the University Hospital of Befelatanana. Cases are represented by patients who had thrombocytosis in complete blood count. Controls had no thrombocytosis in complete blood count and were matched with cases each day of laboratory analysis. There were 105 cases and 105 controls. The blood count was performed on the ABX Pentra 60 hematology automaton and the result was registered in the register book. Those containing incomplete information were excluded from the study. The parameters studied were age, gender, department, clinical information, blood count results and the degree of severity of the thrombocytosis. The data entry and processing was performed on the software Epi-info 3.5.2. We calculated odds ratios (OR) for the association of thrombocytosis with risk factors. The comparison of percentages used the Chi square tests. The statistical significance threshold used was p < 0.05. For ethical reasons, the authorization of the director of establishment was obtained before the data were collected in the registers. The seizure was done anonymously to maintain confidentiality.


In this study, thrombocytosis decreases with age. Subjects older than 60 years are the least affected (OR, 0.16, 95% CI, 0.05-0.49). Women are less affected than men (OR = 0.89, 95% CI, 0.05-1.59). Thrombocytosis is often discovered accidentally during a health check (OR = 4.78, 95% CI, 1.76-13.21) and frequently affects outpatients (Table1).

Table 1: Distribution of cases and controls according to patient characteristics.

Patient’s characteristic Cases (n=105) Controls (n=105) Total OR 95%CI
n % n %
Age (years)
≤19 26 24.8 7 6.7 33 1
20-39 38 36.2 33 31.4 71 0.31 0.11 0.88
40-59 23 21.9 35 33.3 58 0.18 0.06 0.52
≥60 18 17.1 30 28.6 48 0.16 0.05 0.49
Male 53 50.5 50 47.6 103 1
Female 52 49.5 55 52.4 107 0.89 0.5 1.59
Clinical informations
Other clinical information 18 17.1 43 41.0 61 1
Health Check 22 21.0 11 10.5 33 4.78 1.76 13.21
Cardiovascular diseases 11 10.5 15 14.3 26 1.75 0.61 5.05
Dermatoses 8 7.6 6 5.7 14 3.19 0.84 12.37
Infection 26 24.8 15 14.3 41 4.14 1.65 10.53
Pneumopathy 20 19.0 15 14.3 35 3.19 1.23 8.34
Out-patients 22 21.0 15 14.3 37 1
Medicine 73 69.5 82 78.1 155 0.61 0.28 1.33
Infectious diseases 10 9.5 8 7.6 18 0.85 0.24 3.08

The cases present more abnormalities of blood cells than the controls. These abnormalities are mainly represented by anemia (OR=8.01, 95%CI, 3.55-18.5) and hyperleucocytosis (OR=3.73, 95% CI, 1.69-8.37)(Table 2).

Table 2: Distribution of cases and controls according to the others associated anomalies in the complete blood count

Associated anomalies Cases (n=105) Controls (n=105) Total OR 95%CI
n % n %
Red blood cells
Normal levels 54 51.4 94 89.5 148 1
Anemia 46 43.8 10 9.5 56 8.01 3.55 18.5
Polycythemia 5 4.8 1 1.0 6 8.7 0.95 202.14
White blood cells
Normal levels 60 57.1 79 75.2 139 1
Leucopenia 11 10.5 14 13.3 25 1.03 0.4 2.64
Hyperleucocytosis 34 32.4 12 11.4 46 3.73 1.69 8.37

Similarly, severe thrombocytosis is significantly associated with leukocytosis (p = 0.02). This result is depicts in table 3

Table 3: Associated anomalies with the thrombocytosis in the complete blood count.

Associated anomalies Thrombocytosis Total p
Severe (n=48) Mild (n=57)
n % n %
Red blood cells
Normal levels 21 38.9 33 61.1 54 0.15 (NS)
Anemia 23 50.0 23 50.0 46
Polycythemia 4 80.0 1 20.0 5
White blood cells
Low or normal levels 27 38.0 44 62.0 71 0.02
Hyperleucocytosis 21 61.8 13 38.2 34


This study has shown that thrombocytosis decreases with age. Indeed, thrombocytosis in our series are often hereditary thrombocytosis affecting young subjects. These hereditary thrombocytosis are due to a genetic alteration that can be transmitted to offspring. For these inherited thrombocytosis, MPL genetic mutations lead to primary thrombocytosis and THPO gene mutations result in secondary thrombocytosis [3]. Familial thrombocytosis was considered to be an autosomal dominant condition with mutations leading to increased thrombopoietin gene function and increased thrombopoietin production. Recently, other genetic abnormalities have been described involving other mechanisms. Currently, the most common mechanism is the lack of transcription inhibition with excess messenger RNA activity. Cases of familial thrombocytosis without elevation of thrombopoietin have also been reported [4]. Similarly, some acquired thrombocytosis is also common in young subjects such as essential thrombocythemia [4-5]. In the elderly, the literature shows that the complications of thrombocytosis are more common in these subjects. For example, according to the authors, age significantly increases the risk of thrombosis which increases from 1.7% patients / year before 40 years to 6.3% patients / year between 40 and 60 years and 15.1% patients / year after 60 years [3]. In brief, thrombocytosis is frequent in young people but the complications of this pathology are very serious in the elderly.

Depending on the gender, the result of this study is different from that of other studies that show that it is mostly women who are affected by thrombocytosis [4]. The predominance of men in our series is due to the toxic habits of Malagasy men (tobacco, alcohol). These toxins are risk factors for thrombocytosis and thrombotic complications [6].

According to clinical information, it is mostly patients who have had a health check who are most affected by thrombocytosis. Indeed, the majority of thrombocytosis is fortuitous discovery during a blood count [7]. The signs of thrombocytosis appear only at the stage of complications. A patient in apparent good health may have thrombocytosis. Thus, it is always necessary to prescribe a blood count to a patient regardless of the diseases that affect him. Even if there are no apparent diseases, the blood count should always be prescribed during a checkup. Similarly, this study also showed that patients in external consultation are more likely to have thrombocytosis compared to hospitalized patients.

Regarding other abnormalities of the blood count, cases have more abnormalities than controls. Among these abnormalities, polycythemia and hyperleucocytosis were the most frequent. Indeed, thrombocytosis is often reactive in 90% of cases, following an underlying pathology (iron deficiency, inflammatory cause, infection …) [1]. Hence the frequent association of thrombocytosis with hyperleucocytosis. The literature confirms that leukocytes increase when the subject has an infection or inflammatory reaction [8]. Similarly, anemia is a common condition in a hospital setting. It is related to the diet, the mode of life, in the physiological state of the individual [9]. Much pathology may be responsible for the association of anemia with thrombocytosis, such as iron deficiency, which can lead to reactive thrombocytosis [10].

With regard to the severity of thrombocytosis, leukocytosis is frequently associated with severe thrombocytosis with a significant difference. This situation is frequent in severe reactive thrombocytosis as in severe infections. Similarly, some authors have reported the case of severe thrombocytosis and hyperleukocytosis secondary to deep iron deficiency. Thrombocytosis and hyperleukocytosis regressed very rapidly during martial supplementation [10].


This study has highlighted the importance of thrombocytosis, which has been observed frequently in young people and men, and has been incidental found in the blood count during a check-up. Similarly, subjects with thrombocytosis frequently have other abnormalities of the figured elements of the blood compared to controls. This association with other abnormalities may indicate the presence of other underlying pathologies such as infections.This association may also be reactive to other situations such as deep martial deficiency.In brief, the blood count is an essential biological analysis to prescrib for all patients. The discovery of thrombocytosis and other associated abnormalities reveal the severity and prognosis of the associated diseases. The knowledge of this the thrombocytosis can strengthen, adjust or modify the patient’s drug treatments. Thus, patients will have a good follow-up and their life expectancy will be improved.


We would like to thank all the staff of laboratory of University Hospital of Befelatanana and to the laboratory technicians. Similarly, we would like to express our gratitude to the director of establishment for authorizing us to carry out this study.