Originally it was proposed that type II deficiency be further divided into three subgroups IIa, IIb and IIc depending upon which antithrombin functional activity is reduced or retained.
Orixinalmente propúxose que a deficiencia de tipo II fose dividida en tres subgrupos: IIa, IIb e IIc, dependendo de se actividade funcional da antitrombina era reducida ou mantida.