A closed, preassembled and pre-sterilized single-use kit for producing platelet rich plasma for reinfusion to a donor, comprising: - a blood inlet for flowing whole blood to a first stage of a separator; - a two stage unitary spinning membrane separator comprising: - a first stage for receiving whole blood and separating substantially all red blood cells from plasma and platelets through a first filter membrane that substantially blocks red blood cells from passing therethrough, while allowing platelets and plasma to pass therethrough, and - a second stage in fluid communication with the first stage for further separating platelet rich plasma from plasma, which second stage comprises a second filter membrane that substantially blocks platelets therethrough while allowing plasma to pass therethrough; - an outlet in fluid communication with the second stage of the separator for receiving platelet rich plasma, wherein the unitary spinning membrane separator comprises: - a stationary housing having an inner wall defining a hollow interior; - the first generally cylindrical filter membrane and a substrate thereof having a hollow interior; - the second generally cylindrical filter membrane and substrate thereof having a hollow interior; wherein either the first membrane and substrate is present in the interior of the second membrane and substrate or vice versa, and wherein a first gap is defined between them and wherein the inner one of the membranes is rotatable relative to the housing while the outer one of the membranes is stationary so that Taylor vortices may be formed in the first gap, wherein a second gap is formed between an outer one of the membranes and the stationary housing, and a central flow path is defined by the hollow interior of the inner one of the membranes, and wherein first, second and third outlets are in fluid communication with the first gap, the second gap and the central flow path, wherein the first gap is in fluid communication with the blood inlet, and wherein the kit is configured such that plasma and platelets that have passed the first membrane during the first stage to either the second gap or the central flow path leave the housing to an in-process container, from which they are flowed into the first gap for the second stage separation, and the platelet-rich plasma retained in the first gap is then exited from the housing through the first outlet; wherein the first, second and third outlets are selectively closable for controlling direction of flow through the filter membranes. - a blood inlet for flowing whole blood to a first stage of a separator; - a two stage unitary spinning membrane separator comprising: - a first stage for receiving whole blood and separating substantially all red blood cells from plasma and platelets through a first filter membrane that substantially blocks red blood cells from passing therethrough, while allowing platelets and plasma to pass therethrough, and - a second stage in fluid communication with the first stage for further separating platelet rich plasma from plasma, which second stage comprises a second filter membrane that substantially blocks platelets therethrough while allowing plasma to pass therethrough; - a first stage for receiving whole blood and separating substantially all red blood cells from plasma and platelets through a first filter membrane that substantially blocks red blood cells from passing therethrough, while allowing platelets and plasma to pass therethrough, and - a second stage in fluid communication with the first stage for further separating platelet rich plasma from plasma, which second stage comprises a second filter membrane that substantially blocks platelets therethrough while allowing plasma to pass therethrough; - an outlet in fluid communication with the second stage of the separator for receiving platelet rich plasma, - a stationary housing having an inner wall defining a hollow interior; - the first generally cylindrical filter membrane and a substrate thereof having a hollow interior; - the second generally cylindrical filter membrane and substrate thereof having a hollow interior;