The present invention generally relates to systems and methods for delivering and/or withdrawing a substance or substances such as blood or interstitial fluid, from subjects, e.g., from the skin and/or from beneath the skin. In one aspect, the present invention is generally directed to devices and methods for withdrawing or extracting blood from a subject, e.g., from the skin and/or from beneath the skin, using devices containing a fluid transporter (for example, one or more microneedles), and a storage chamber having an internal pressure less than atmospheric pressure prior to receiving blood. In some cases, the device may be self-contained, and in certain instances, the device can be applied to the skin, and activated to withdraw blood from the subject. The device, in some cases, may be interfaced with external equipment to determine an analyte contained within a fluid contained within or collected by the device. For example, the device may be mounted or engaged on an external holder, the device may include a port for transporting fluid out of the device, the device may include a window for interrogating a fluid contained within the device, or the like. The device, or a portion thereof, may then be processed to determine the blood and/or an analyte within the blood, alone or with an external apparatus. For example, blood may be withdrawn from the device, and/or the device may contain sensors or agents able to determine the blood and/or an analyte suspected of being contained in the blood. Other aspects of the present invention are directed at other devices for withdrawing blood (or other bodily fluids, e.g., interstitial fluid), kits involving such devices, methods of making such devices, methods of using such devices, and the like.
