What does the medical abbreviation hb solu plus rflx frac mean?

This is a type of solubility testing for sickle cell disease. It is very specific for this disease and several combinations sickle cell / thalassemia variants but inadequate for screening and fail to identify important transmissible hemoglobin gene abnormalities - particularly in the prenatal setting when looking for those that affect fetal outcome (eg, Hb C trait, β-thalassemia trait, Hb E trait, Hb B trait, Hb D trait).