Numerous medical operations employ blood transfusions, requiring X-ray irradiated blood for safety concerns. Current irradiation techniques can be significantly improved by replacing standard visual indicators with wireless dosimeter tags that automate the process, reducing inefficiencies and eliminating blood wastage. A key requirement of the proposed dosimeter tag is flexible and efficient antennas that can be mounted on blood bags. This paper presents the design of a low-cost inkjet-printed dipole antenna on flexible Kapton substrate for a 2.45 GHz RFID dosimeter tag. The tag is to be used in a lossy blood environment, which can severely affect antenna radiation performance. To mitigate this, the concept of artificial magnetic conductor (AMC) unit cells is investigated for best impedance and gain performance. When integrated with a dipole radiator, the fabricated AMC-backed antenna maintains broadside radiation with gains of 4.1 dBi to 4.8 dBi under planar and bending conditions, and on a lossy blood bag. In a rectenna configuration, the antenna can power sensors for ranges up to 1m. Measured output dc voltages up to 1.7 V are achieved across a 25 kΩ resistor. This antenna design is flexible, compact, efficient on lossy structures and suitable for direct integration with biomedical sensing chips.