A method for purifying Apo A-I is provided including the steps of providing a solution comprising Apo A-I and guanidine hydrochloride and filtering the solution through a filter having a pore size in a range from 15 nrn to 35 nm to thereby reduce viral contamination of the Apo A-I. An Apo A-f preparation is provided having at least a 12 log LRV (log reduction value) for a parvovirus; and/or at least 9 log LRV for a non-enveloped virus; and/or at least 8.5 log LRV for a lipid enveloped virus. Also provided are pharmaceutical compositions and reconstituted high density lipoprotein formulation comprising Apo A-I and methods of treating diseases disorders or conditions.