A system, method and apparatus for determining a physiological condition within a mammal based on pH and/or temperature measurements. In one aspect, the invention is directed to an apparatus for measuring a physiological condition within a mammal comprising: a tubular housing extending along a longitudinal axis from a distal end to a proximal end, the housing having an internal cavity a first opening in the elongated housing forming a first passageway into the internal cavity an ion-sensitive field effect transistor (ISFET) for measuring pH within a body lumen of the mammal, the ISFET positioned in the internal cavity, the ISFET aligned with the first opening so that at least a portion of the ISFET is exposed via the first opening and a first seal between the ISFET and the housing forming a hermetic seal about a perimeter of the first opening.
