Hemophilia B, an atypically heavy bleeding during a routine newborn test

Hemophilia B is a blood disorder caused by a deficiency of factor IX. Although it is usually diagnosed when the infant starts crawling or walking through the detection of hemarthrosis or  muscle bleeds, in this case the onset occurred at 3 days of age with detection of heavy atypical bleeding during a routine test. The examination and additional testing (blood count, coagulation, ultrasound of soft tissue and large joints) did not evince severe disease. Factor IX, which determines the severity, increased from 1% to 3% in 24 hours, so treatment was not required.