Methods and systems for determining the concentration of one or more analytes from a sample such as blood or plasma are described. The systems described herein can be configured to withdraw a sample from a source of fluid, direct a first portion of the withdrawn sample to an analyte monitoring system and return a second portion of the sample. The analyte monitoring system can be connected to the fluid source via a connector that is configured to improve fluid flow and reduce blood clotting risk. These goals can be accomplished, for example, by employing coatings in or on a connector, positioning a resilient substance at or near the junction, by reducing dead space volume, by using resiliency to improve fit, by extending a portion of one connector to better mate with a portion of another connector, etc.