Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
Certain medical states or conditions of a human body can be detected using sensors disposed within the human body (e.g., implanted within and/or penetrating skin of the human body) and/or by extracting a fluid or tissue (e.g., by extracting a sample of blood using, e.g., a syringe, by biopsying a portion of tissue) for analysis outside of the human body.  Some medical states or conditions can change slowly, occur rarely, or otherwise indicate that monitoring of the human body over an extended period of time is preferred.  For example, a level of glucose in blood of an individual with diabetes could be monitored at a plurality of points in time.  A sensor implanted within the human body could enable long-term monitoring of a medical state or condition of the body of a wearer while allowing the wearer to perform activities of daily living, to travel, to commute, or to engage in other activities with minimal interruption.  Additionally or alternatively, a target fluid (e.g., blood) could be extracted transdermally (e.g., using a syringe, lancet, or other instrument) a plurality of times.  Such monitoring could be performed preventatively, e.g., to monitor an otherwise healthy wearer's health state over time to enable early detection of an adverse medical condition, to develop data describing a ‘healthy’ baseline state of the wearer, or to enable other applications.  Medical states or conditions of a human body monitored via detection of one or more properties of a fluid or tissue within the human body can include electrolyte concentrations (e.g., chloride, potassium, calcium, sodium), glucose or other metabolite concentrations (e.g., urea, creatinine), blood oxygenation, or other information about the body of a wearer.