Abstract: Diagnostic testing systems and related methods employ actuation pressure-based control during fluid transfer within a test cartridge. A method of operating a cartridge to process a biological sample includes coupling an actuation port of the cartridge with a pump assembly of a portable analyzer. A transfer operation of the pump assembly induces airflow through the actuation port so as to displace an aliquot of the sample solution along a fluid channel. A control unit monitors a pressure signal indicative of a pressure of air displaced by the pump assembly. The transfer operation is stopped in response to a change in the pressure signal indicative of contact of the aliquot of the sample solution with a hydrophobic staging vent.