Abstract: Device including migration membrane, conjugate pad on migration membrane, plasma separation membrane on conjugate pad, pre-filter on plasma separation membrane. Migration membrane has test line configured for loading one or plurality of capture antibodies having specific binding affinity for assay target. Migration membrane configured for allowing lateral flow of blood plasma or serum across migration membrane to test line. Conjugate pad configured for loading one or plurality of detection antibodies having specific binding affinity for assay target. Plasma separation membrane configured for allowing passage of blood plasma or serum and trapping erythrocytes. Pre-filter configured for loading assay sample including erythrocytes and either or both blood plasma and blood serum. Pre-filter configured for allowing passage of blood plasma or serum through pre-filter and causing lateral flow of blood plasma or serum within pre-filter. Method includes providing device and carrying out diagnostic assay cycle.