Kiladjian et al state that the results of their study showed a standardized mortality ratio (SMR) of 1.0 and a 15-year risk of thrombosis of 21.8% in 164 polycythemic patients.
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In our cohort of 396 patients with polycythemia vera, SMR was 1.6 and the 15-year risk of thrombosis was 27%.2
The patient cohort included 130 patients with polycythemia vera and 34 individuals with idiopathic erythrocytosis. Idiopathic erythrocytosis represents a grey zone between diagnosis of polycythemia vera and that of secondary erythrocytosis.
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The fact that 20% of patients in the Kiladjian study were classified as idiopathic erythrocytosis might explain the lower SMR and the slightly lower risk of thrombosis compared with our study that included only patients with polycythemia vera.To estimate SMR, Kiladjian et al compared the observed mortality with the probability of death in an age- and sex-matched French population. Usually, SMR is calculated by applying the mortality rates (ie, the incidence of death), and not the probability of death, in the reference population in comparison with the study cohort. In contrast to the French study, we used age-, sex-, and calendar-year specific reference rates to calculate the SMR.
2
This allows for more reliable estimates especially when the cohort has a long period of recruitment, because mortality rates tend to vary with time.Kiladjian et al also report an incidence of thromobosis even lower than that observed in the French matched-control population. This statement, however, is not supported by appropriate data because a direct comparison of the incidence of thrombosis between patients and the control population is not reported.
Finally, concerning the well-known potential biases of retrospective studies, in the cohort of 396 patients followed at our centres, the rate of patients lost to follow-up was as low as 2.5%, even lower than that reported by the prospective study by Kiladjian et al (11.6%).
References
- Long-term outcomes of polycythemia vera patients treated with pipobroman as initial therapy.Hematol J. 2003; 4: 198-207
- Life expectancy and prognostic factors for survival in patients with polycythemia vera and essential thrombocythemia.Am J Med. 2004; 117: 755-761
- Idiopathic erythrocytosis-a declining entity.Br J Haematol. 2001; 115: 774-781
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© 2005 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
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- Is life expectancy of polycythemia vera patients clearly different from that of the general population?The American Journal of MedicineVol. 118Issue 5
- PreviewIn a recent issue of the American Journal of Medicine, Passamonti et al reported a significantly higher mortality for polycythemia vera (PV) patients than in a sex-, age-, and calendar year-matched Italian general population in a retrospective analysis of 396 PV patients, using standardized mortality ratio (SMR).1 Thrombosis was the most frequent complication and the main cause of death, and a history of thrombosis was the only adverse prognostic factor for survival. By contrast, survival of patients with essential thrombocythemia was similar to that of the general population.
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