Milligram per cent is a traditional symbol used to denote a unit of measure of concentration. The traditional use of the 'mg%' symbol was meant to indicate the mass (in milligrams) of that chemical in 100 milliliters of solution (e.g., blood). The meaning of the symbol 'percent' is 1/100, therefore the accurate meaning of the notation 'mg%' is 'mg/100', which is a unit of mass, not a concentration. Therefore, for dimensional analysis purposes, when denoting a concentration of mass divided by volume, it has largely been replaced by units such as 'mg/dL' or the International System of Units equivalent.
For example, a plasma ethanol concentration incorrectly denoted as 0.1 mg% can be written as '0.1 mg/dL' (or '1 mg/L', etc.) meaning a mass of 0.1 milligrams of ethyl alcohol per 100 milliliter volume of plasma.