Kits and methods provide for the isolation of white blood cells from bodily fluids. In one exemplary aspect, a method for isolating white blood cells from blood includes the act of adding a blood sample to a separation tube having a distal end, a proximal end, and a valve located proximate said proximal end, said valve being configured to transition between at least first, second, and third positions. The method also includes the act of removably attaching a cap to the distal end, centrifuging the separation tube with the valve in the first position, removing the cap at the distal end of the separation tube and removably attaching a first syringe to the proximal end, switching the valve to the second position and withdrawing, via the first syringe, a red blood cell sediment. The method also includes the act of switching the valve to the first position and removing the first syringe, adding a small volume of buffer to the separation tube, removably attaching a cap to the distal end and centrifuging the separation tube and removing the cap at the distal end of the separation tube and removably attaching a second syringe to the proximal end. Additional acts include switching the valve to the second position, withdrawing the remaining red blood cell sediment via the second syringe and switching the valve to the first position and removing the second syringe.
