The invention relates to an apparatus and method to determine and monitor the flow rates and volume of fluids excreted or secreted by the body. The apparatus includes: a measuring unit comprising a conduit made of a material having a low thermal conductivity and supporting at least two thermistors that includes an upstream thermistor serving as a compensation thermistor and a downstream thermistor located as far downstream as possible from the upstream thermistor and pre-heated to and kept at pre-defined temperature which is warmer than the fluid temperature to be metered. The apparatus further includes a power supply for applying small electric voltages to the thermistors to enable generation of an electric signal and a control and display unit being operatively connected to the measuring unit.
