Directorate of Anaesthesia and Intensive Care, North Staffordshire Hospital, Stoke-on-Trent ST4 6QG, UK*Corresponding author
Accepted for publication: August 13, 2001
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Abstract |
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Br J Anaesth 2001; 87: 9268
Keywords: intensive care, mortality; blood, platelets, thrombocytosis
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Introduction |
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The purpose of this study was to explore the incidence of thrombocytosis and its relation to duration of ICU stay and outcome. Thrombocytosis may serve as an additional variable in prediction of outcome in ICU patients.
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Methods and results |
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Continuous variables are expressed as number and percentage of the group from which they were obtained, or median and interquartile range. Continuous variables were analysed using the KruskalWallis test. The MannWhitney test was used to compare duration of ICU stay between patients with early and late onset of thrombocytosis. Discrete variables were analysed using chi-squared tests. Statistical analyses were performed using StatView® version 4.02 for Macintosh and a P value of <0.05 was considered significant.
A total of 231 patients were admitted during the study period: to the GICU, 104 and to the TICU, 127. Four patients with no documented platelet count and one patient transferred to an ICU in another hospital were excluded. The platelet count of 226 patients and admission category, predicted mortality, ICU outcome and hospital outcome were analysed (Table 1). Thrombocytosis, defined as a platelet count of greater than 450x109 litre1 on at least one occasion, was observed in 49 patients (21.7%). The median onset of thrombocytosis was 7 (111) days after ICU admission, although 39% of patients either had thrombocytosis at ICU admission or developed this within 4 days. Patients with at least one platelet count higher than 450x109 litre1 had lower ICU and hospital mortality but a longer duration of ICU stay, despite similar predicted mortality (Table 1). The median (range) duration of ICU stay (18.5, 1333 days) was significantly longer in patients who developed thrombocytosis after 4 or more days in the ICU compared with those with an earlier thrombocytosis (3, 16 days; P<0.0001), although the mortality of these two subgroups did not differ significantly.
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Comment |
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We are unaware of any previous literature describing the association between a high platelet count and outcome in critically ill patients. We found that a platelet count higher than 450x109 litre1 on at least one occasion during the ICU stay was associated with lower ICU and hospital mortality. This was equally true for patients presenting to ICU with an established thrombocytosis and for those developing it later. Indeed, a small cohort of patients (n=14) developed a thrombocytosis after presenting with an initial platelet count of less than 150x109 litre1. These patients were included with the thrombocytosis group, but even when analysed separately, they were still associated with a more favourable outcome compared with patients without a thrombocytosis. As thrombocytopenia is associated with poor outcome,2 we compared our patients with thrombocytosis against patients with thrombocytopenia as well as those with a normal platelet count throughout; outcome was more favourable compared with either group. Overall, thrombocytosis was associated with a prolonged ICU stay, although this was far less marked in patients presenting to ICU with thrombocytosis or developing it at an early stage.
Despite these findings, this study has some limitations. It is a retrospective study. Some patients were not on the ICU for sufficient time for all data required to calculate predicted mortality to be collected. However, the distribution of these patients did not differ between the three groups defined by platelet counts. Being the major trauma receiving hospital in the region, the proportion of patients admitted with multiple trauma including head injury requiring neurosurgery is high, which is the reason for grouping these categories of patient together in our study. Thrombocytosis was more common in this patient category.
In conclusion, thrombocytosis is a common finding in ICU. It appears to be associated with lower ICU and hospital mortality but longer duration of ICU stay. It may serve as an additional variable in predicting outcome in ICU patients. A large prospective study is required to confirm these findings.
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References |
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2 Vanderschueren S, De Weerdt A, Malbrain M, et al. Thrombocytopenia and prognosis in intensive care. Crit Care Med 2000; 28: 18716[ISI][Medline]
3 Buss DH, Cashell AW, OConnor ML, Richard F, II, Case LD. Occurrence, etiology, and clinical significance of extreme thrombocytosis: A study of 280 cases. Am J Med 1994; 96: 24753[ISI][Medline]
4 Schmuziger M, Christenson JT, Maurice J, Simonet F, Velebit V. Reactive thrombocytosis after coronary bypass surgery. An important risk factor. Eur J Cardiothorac Surg 1995; 9: 3937[Abstract]
5 Nijsten MWN, ten Duis H-J, Zijlstra JG, et al. Blunted rise in platelet count in critically ill patients is associated with worse outcome. Crit Care Med 2000; 28: 38436[ISI][Medline]