To investigate whether the elevation of factor VIII coagulant activity observed in children with poor control of diabetes is due to increased levels of the factor VIII coagulant moiety of the factor VIII complex or reflects activation of the factor VIII coagulant moiety, factor VIII coagulant activity (VIII C), factor VIII coagulant antigen (VIM C:Ag), and factor VIII-related antigen (VIII R:Ag) were determined in 75 insulin-dependent children. All children were without signs of vascular disease based on negative funduscopy, negative fluorescein angiography, normal serum creatinine levels, and absence of proteinuria. Children with poor actual control of diabetes had significantly higher VIII C values than did children with good actual control of diabetes based on HbA1 values, but VIM C:Ag values did not differ in children with good or poor actual control of diabetes. A significant elevation of VIM C over VIII C:Ag values was observed in children with poor actual control of diabetes, but no elevation of VIII C over VIM C:Ag was found in children with good actual control. VIM R:Ag values were higher in children with poor actual control. VIM C, VIM C:Ag, and VIII R:Ag did not differ significantly in children with short or long duration of clinical diabetes.

Our observation of significantly higher VIM C values, than VIM C:Ag levels strongly suggests intravascular activation of the factor VIM coagulant moiety during poor diabetes control. The process leading to activation of the coagulant moiety seems to be different from the process leading to the elevation of the other moiety of the factor VIM complex, the factor VIII-related antigen, in diabetic subjects.

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