A blood sampling device useful for collecting a blood sample from a separate vascular access device is described herein. The blood sampling device includes a body shaped and sized for partial insertion into a separate vascular access device. The body includes a reservoir defined within the body, which has an internal volume sufficient to contain enough blood for use in a diagnostic blood test. The body also includes a gas permeable vent disposed on the body, in which the gas permeable vent is in gaseous communication with the reservoir. When connected to a separate vascular access device the blood sampling device collects a blood sample as blood flows into the reservoir from the separate vascular access device and as gases pass out the reservoir via the gas permeable vent.