Abnormal HDL cholesterol concentration Abnormal HDL subfraction concentration 2019-03-02T13:28:34Z An abnormal concentration of an HDL subfraction, which can be determined by methods such as electrophoresis followed by densitometric determination of the areas under the peaks. Large HDL subfractions are defined as HDL1 (greater than 12 nm), HDL2b (9.7-12 nm), and HDL2a (8.8-9.69 nm). Small HDL subfractions are defined as HDL3a (8.2-8.79 nm), HDL3b (7.8-8.19 nm), and HDL3c (7.20-7.79 nm). Traditionally, HDL is separated into two major subclasses (HDL2 and HDL3), but depending on the separation method used, u[ to 10 subfractions have been reported.