156 Part 2 (Chapters 4, 5 and 6) focused on different aspects of bleeding in persons with OI, such as the prevalence of anamnestic increased bleeding tendency and possible underlying coagulation disorders. In Chapter 4, a pilot study was conducted on 22 adults with OI to explore bleeding tendencies, for the first time since 40 years. Both an extensive questionnaire (Self-BAT version of the ISTH-BAT) and laboratory blood tests were used to identify bleeding tendencies and to see whether there was an indication of underlying coagulation disorders. Four patients exhibited increased bleeding tendencies, but no underlying coagulation problems were found. Abnormal fibrinolysis was observed in two patients without a history of bleeding tendencies. This pilot study did not provide definitive evidence of increased bleeding tendencies or coagulation disorders in this group of patients with OI. Chapter 5 examined anamnestic increased bleeding tendency in a large cohort using the self-administered ISTH-BAT (Self-BAT) questionnaire. In total, 195 questionnaires completed by persons with OI were included for analyses in this chapter to determine which bleeding symptoms were most common and which were most clinically relevant. The main finding was that 81 of 195 patients (42%) showed increased bleeding tendency, which was significantly higher than in an average population. Therefore, the main conclusion was that bleeding tendency is actually an important problem in people with OI. Since patients with OI frequently undergo surgery and often require tooth extractions, it is essential to be alert for bleeding during these procedures. It has been noted that such procedures often require major interventions to stop bleeding. Moreover, it appears that heavy menstrual bleeding and postpartum bleeding are common. For such types of bleeding, therapies to reduce the severity of bleeding are often available. Therefore, the advice arising from this chapter was to properly identify the increased bleeding tendency in individual OI patients with a structured history (ISTH-BAT) and to apply interventions to reduce bleeding at individual bases. In Chapter 6, a selection of patients was made with the highest bleeding tendencies based on the Self-BAT, as described in Chapter 5. Laboratory investigations similar to Chapter 4 were then performed in these patients. These investigations included the measurement of bleeding time, which might be the most sensitive test for the effects of collagen deficiency in the vascular wall. Of 11 selected OI patients with the highest bleeding tendency, two patients indeed had a prolonged bleeding time. In addition, abnormalities were found in fibrinogen ( n =1), factor VIII (n = 2) and von Willebrand factor (n = 1). Abnormalities in platelet function were also observed (n = 6). However, all
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