A valve system in a fluidic cartridge for metering a liquid sample in a sample processing region, comprising: a fluid pathway (C310a) for passing a liquid sample therethrough from an upstream end to a downstream end; a sample processing chamber (C302a) within the fluid pathway having an inlet valve (C301a) upstream of the sample processing chamber and an outlet valve (C303a) downstream of the sample processing chamber (C302a); a downstream sample processing region (C304a) within the fluid pathway (C310a) downstream of the outlet valve (C303a); and a bypass channel (C305a) coupled to the fluid pathway (C310a) at a junction between the outlet valve (C303a) and the downstream sample processing region (C304a), the valve system configured such that surplus liquid sample downstream of the outlet valve may be evacuated through the bypass channel when the outlet valve is closed, thereby leaving a metered volume of liquid sample in the fluid pathway between the inlet valve and the downstream sample processing region, wherein the bypass channel (C305a) is connected to the fluid pathway immediately downstream of the outlet valve (C303a) so as to minimise or eradicate a deadleg between the outlet valve and the bypass channel; and wherein the fluid pathway further comprises a compressible element (C306a) downstream of the downstream sample processing region (C304a), the compressible element (C306a) configured to become increasingly biased against fluid upstream of the compressible element (C306a) as the liquid sample passes through the open outlet valve (C303a) so as to increase the pressure in the fluid pathway (C310a), such that surplus liquid sample downstream of the outlet valve (C303a) may be expelled from the fluid pathway (C310a) and into the bypass channel (C305a) by the compressible element (C306a) when the outlet valve (C303a) is closed and whilst the pressure in the bypass channel (C305a) is less than the pressure in the fluid pathway (C310a). a fluid pathway (C310a) for passing a liquid sample therethrough from an upstream end to a downstream end; a sample processing chamber (C302a) within the fluid pathway having an inlet valve (C301a) upstream of the sample processing chamber and an outlet valve (C303a) downstream of the sample processing chamber (C302a); a downstream sample processing region (C304a) within the fluid pathway (C310a) downstream of the outlet valve (C303a); and a bypass channel (C305a) coupled to the fluid pathway (C310a) at a junction between the outlet valve (C303a) and the downstream sample processing region (C304a), the valve system configured such that surplus liquid sample downstream of the outlet valve may be evacuated through the bypass channel when the outlet valve is closed, thereby leaving a metered volume of liquid sample in the fluid pathway between the inlet valve and the downstream sample processing region, wherein the bypass channel (C305a) is connected to the fluid pathway immediately downstream of the outlet valve (C303a) so as to minimise or eradicate a deadleg between the outlet valve and the bypass channel; and wherein the fluid pathway further comprises a compressible element (C306a) downstream of the downstream sample processing region (C304a), the compressible element (C306a) configured to become increasingly biased against fluid upstream of the compressible element (C306a) as the liquid sample passes through the open outlet valve (C303a) so as to increase the pressure in the fluid pathway (C310a), such that surplus liquid sample downstream of the outlet valve (C303a) may be expelled from the fluid pathway (C310a) and into the bypass channel (C305a) by the compressible element (C306a) when the outlet valve (C303a) is closed and whilst the pressure in the bypass channel (C305a) is less than the pressure in the fluid pathway (C310a).