A medical fluid pumping system comprising: a medical fluid pump; a reference chamber (VSL, VSR) connected fluidly to the medical fluid pump; a first pressure chamber (POS T) connected fluidly to the medical fluid pump and the reference chamber; a second pressure chamber (POS P-L, POS P-R) connected fluidly to the medical fluid pump and the reference chamber; first (X-POS T) and second (X-POS P-L, X-POS P-R) pressure sensors connected operably to the first and second pressure chambers, respectively; and at least one processor operable with the pressure sensors to calculate a volume of gas (V gas,full) in the medical fluid pump prior to a pump-out stroke using a reading from the first pressure sensor after exposing the pump to gas pressure from the first pressure chamber and to use the calculated volume of gas in combination with a known volume of the second pressure chamber and a pressure decay reading (P POS P,t) taken via the second pressure sensor during the pump-out stroke to calculate at least one volume of fluid pumped during the pump-out stroke (V fluid,t), characterized in that the at least one processor is configured after the pump-out stroke to: (i) calculate a volume of gas in the medical fluid pump using a reading from the first pressure sensor after exposing the pump to gas pressure from the first pressure chamber, (ii) calculate a first total volume of fluid pumped via the pump-out stroke by subtracting the volume of gas in the medical fluid pump after the pump-out stroke from the volume of gas in the medical fluid pump prior to the pump-out stroke, (iii) calculate a second total volume of fluid pumped using a final pressure decay reading taken via the second pressure sensor, and (iv) compare the first and second total fluid volumes pumped via the pump-out stroke. a medical fluid pump; a reference chamber (VSL, VSR) connected fluidly to the medical fluid pump; a first pressure chamber (POS T) connected fluidly to the medical fluid pump and the reference chamber; a second pressure chamber (POS P-L, POS P-R) connected fluidly to the medical fluid pump and the reference chamber; first (X-POS T) and second (X-POS P-L, X-POS P-R) pressure sensors connected operably to the first and second pressure chambers, respectively; and at least one processor operable with the pressure sensors to calculate a volume of gas (V gas,full) in the medical fluid pump prior to a pump-out stroke using a reading from the first pressure sensor after exposing the pump to gas pressure from the first pressure chamber and to use the calculated volume of gas in combination with a known volume of the second pressure chamber and a pressure decay reading (P POS P,t) taken via the second pressure sensor during the pump-out stroke to calculate at least one volume of fluid pumped during the pump-out stroke (V fluid,t), (i) calculate a volume of gas in the medical fluid pump using a reading from the first pressure sensor after exposing the pump to gas pressure from the first pressure chamber, (ii) calculate a first total volume of fluid pumped via the pump-out stroke by subtracting the volume of gas in the medical fluid pump after the pump-out stroke from the volume of gas in the medical fluid pump prior to the pump-out stroke, (iii) calculate a second total volume of fluid pumped using a final pressure decay reading taken via the second pressure sensor, and (iv) compare the first and second total fluid volumes pumped via the pump-out stroke.