126 Clotting (formation) time, firmness and fibrinolysis All Extem results for CT, CFT and MCF fell within the reference ranges. ExtemML results were abnormal in 5/20 cases. ExtemCFT results were significantly shortened for the group with the highest bleeding scores on the self-BAT (p = 0.043). ExtemMCF results were significantly higher for the group with the highest bleeding scores on the self-BAT (p = 0.041). Results for IntemCT were prolonged in 4/20 cases. IntemCFT results were shortened in 9/20 cases. IntemMCF results all fell within the reference ranges. IntemML results were abnormal in 3/20 cases. IntemCFT results were significantly shortened for the group with the highest bleeding scores on the self-BAT (p = 0.027). In 1/20 cases, AptemCT result was prolonged. AptemCFT results were shortened in 3/20 cases. AptemMCF results all fell within reference ranges. AptemML results were abnormal in 3/20 cases. AptemCFT results were significantly shortened for the group with the highest bleeding scores on the self-BAT (p = 0.023). AptemMCF results were significantly higher for the group with the highest bleeding scores (p = 0.046). Signs for hyperfibrinolysis were negligible. Discussion Patients with OI are believed to have an increased risk of bleeding symptoms. However, an underlying clarification has not yet been found. In this study we compared 11 adult OI patients with a high bleeding score to 9 OI patients with a normal/low bleeding score. A total of 23 laboratory test variables were analysed. No significant differences between the two groups were found. A range of mild abnormalities in the total group of 20 OI patients were found, most noticeable being abnormal platelet function in 30% of the cases, regardless of the bleeding score. The first literature on affected platelet function in OI is dated 1957 by Siegel et al. 6. Furthermore, Estes et al. described large platelets 8 and Hathaway et al. observed abnormalities in platelet function 7. In patients with OI, the impaired biosynthesis of collagen could potentially disrupt platelet function. Artoni et al. speculated that an altered structure of the vessel wall due to abnormal collagen biosynthesis may lead to activation and exhaustion of the platelets 5. A comparable mechanism is decribed by Boneu et al. in 1987, describing the role of red blood cells in platelet-vessel
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