A biological fluid sampling system comprising: a biological fluid transfer device adapted to receive a multi-component blood sample , the biological fluid transfer device comprising: a housing having an inlet port and a transfer port , the inlet port and the transfer port in fluid communication; a mixing channel in fluid communication with the inlet port and the transfer port , and a blood separation element disposed between the inlet port and the transfer port , the blood separation element adapted to restrain a first component of the multi-component blood sample and allow a second component of the multi-component blood sample to pass therethrough, characterized in that the mixing channel is shaped to promote mixing of the multi-component blood sample ; the biological fluid sampling system further comprises: a first interface removably connectable to the inlet port of the biological fluid transfer device , the first interface- configured for connection to a first biological fluid collection device; a second interface removably connectable to the inlet port of the biological fluid transfer device , the second interface configured for connection to a second biological fluid collection device; and a packaging member having a compartment sized and adapted to receive the biological fluid transfer device , the first interface , and the second interface therein, wherein the first interface is different from the second interface . a biological fluid transfer device adapted to receive a multi-component blood sample , the biological fluid transfer device comprising: a housing having an inlet port and a transfer port , the inlet port and the transfer port in fluid communication; a mixing channel in fluid communication with the inlet port and the transfer port , and a blood separation element disposed between the inlet port and the transfer port , the blood separation element adapted to restrain a first component of the multi-component blood sample and allow a second component of the multi-component blood sample to pass therethrough, a housing having an inlet port and a transfer port , the inlet port and the transfer port in fluid communication; a mixing channel in fluid communication with the inlet port and the transfer port , and a blood separation element disposed between the inlet port and the transfer port , the blood separation element adapted to restrain a first component of the multi-component blood sample and allow a second component of the multi-component blood sample to pass therethrough, characterized in that the mixing channel is shaped to promote mixing of the multi-component blood sample ; the biological fluid sampling system further comprises: a first interface removably connectable to the inlet port of the biological fluid transfer device , the first interface- configured for connection to a first biological fluid collection device; a second interface removably connectable to the inlet port of the biological fluid transfer device , the second interface configured for connection to a second biological fluid collection device; and a packaging member having a compartment sized and adapted to receive the biological fluid transfer device , the first interface , and the second interface therein, wherein the first interface is different from the second interface . a first interface removably connectable to the inlet port of the biological fluid transfer device , the first interface- configured for connection to a first biological fluid collection device; a second interface removably connectable to the inlet port of the biological fluid transfer device , the second interface configured for connection to a second biological fluid collection device; and a packaging member having a compartment sized and adapted to receive the biological fluid transfer device , the first interface , and the second interface therein, wherein the first interface is different from the second interface . <EOS>