A concentrator is used for concentrating a fluid, particularly a plasma component out of blood, for treatment of a patient. The concentrator apparatus includes a main housing defining a centrifuge chamber, that also holds the filter. The concentrator allows viewing of the fluid after centrifuging, with an outlet port positionable at a height corresponding to the level of the fraction of the fluid to be further concentrated. Once the fluid is centrifuged, a portion of the fluid is drawn through the outlet, and then pressured past the filter to further concentrate the fluid using the same vessel as used for centrifuging. The same plunger is preferably used to draw centrifuged fluid from the centrifuge chamber as to pressure the centrifuged fluid past the filter.