Dr Smith described how Factor IX concentrate was thought to carry the risk of venous thrombosis at the site of infusion (possibly fatal) when administered at a high dosage. Similarly, reports of thrombosis occurred at higher frequency in the early 1980s supposedly due to activated Factor IX. Clinicians had to choose between unheated Factor IX and run the risk of transmitting NANBH or AIDS, or buying heated Factor IX concentrate where it wasn't tested for thrombogenicity.