In some embodiments, the present invention generally relates to the separation of blood within a device to form plasma or serum. In some embodiments, the present invention generally relates to the removal of fluids, such as blood, contained within a device. For example, a device may be applied to the skin of a subject to receive blood from the subject and pass the blood through a separation membrane, which separates the blood into plasma and a portion concentrated in blood cells. As another example, blood or plasma may be allowed to clot within the device and serum (the unclotted portion of the blood) may be withdrawn from the device. The device may contain, in some cases, a vacuum source such as a pre-packaged vacuum to facilitate receiving of blood and/or passage of the blood through the separation membrane to produce plasma or serum.
