121 Chapter 6 Fibrinolysis was determined through semi-automated thromboelastometry (ROTEM® sigma; Werfen Netherlands, Breda, the Netherlands). Clot formation and lysis were determined after adding reagents activating the internal or external coagulation pathway. Maximum lysis (ML) was optically measured as the percentage reduction of clot firmness within 60 minutes. Other ROTEM® parameters such as clotting time (CT), clot formation time (CFT), and maximum clot firmness (MCF) were also analysed. Statistical analysis Variables were tested for normal distribution using the Shapiro Wilk test and Q-Q plots. Differences in means comparing OI patients with the highest bleeding scores versus normal bleeding scores were determined for normally distributed data using the independent t test (CI 95%). Non-normal distributed data were tested using the Mann-Whitney test (CI 95%). All the data obtained from the bleeding time research and laboratory blood sampling were collected and analysed in SPSS 24. Results Clinical characteristics Of the 23 patients with high self-BAT-scores who were invited to participate in the study, four patients did not want to participate in additional laboratory tests. Twelve patients were excluded: two patients because of known pre-existing Von Willebrand disease, five patients due to use of anticoagulants, and one patient because of a long travelling time (>5h). This resulted in 11 patients who were included in the group with the highest bleeding score on the self-BAT questionnaire. This subgroup consisted of nine females and two males, with a mean age of 44.5 years (SD 12.1). Ten patients in this group had OI type 1, one patient in this group had OI type 4. Of the 19 patients with low bleeding scores on the self-BAT, ten did not want to participate. The subgroup of nine patients with a low bleeding score consisted of five males and four females with a mean age of 37.4 years (SD 13.8). Seven patients had OI type 1, one patient OI type 3, and one patient OI type 4 (Table 1). The selection process resulted in laboratory tests in 20 individuals with equal male/female ratios and about the same average age compared to the total population of 195 OI patients (43.7 years; SD 15.6). All participants were of Caucasian origin.
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