Determining a quantity of an analyte in a blood sample

A method of determining a quantity of an analyte in a blood sample using a cartridge, wherein the cartridge is operable for being spun around a rotational axis, wherein the cartridge comprises:

• an inlet for receiving the blood sample;
• a blood separation chamber for separating blood plasma from the blood sample, wherein the blood separation chamber is fluidically connected to the inlet;
• a processing chamber containing at least one reagent comprising at least one specific binding partner which is operable to bind to the analyte to form at least one analyte specific binding partner complex;
• a first valve structure connecting the blood separation chamber to the processing chamber;
• a measurement structure for enabling measurement of the quantity of the analyte, wherein the measurement structure comprises a chromatographic membrane, wherein the chromatographic membrane comprises an immobilized binding partner for direct or indirect binding of the analyte or the at least one analyte specific binding partner complex, wherein the measurement structure further comprises an absorbent structure, wherein the absorbent structure is nearer to the rotational axis than the membrane;
• a second valve structure connecting the processing chamber to the measurement structure;
• a fluid chamber filled with a washing buffer, wherein the fluid chamber is fluidically connected to the measurement structure, wherein a seal keeps the washing buffer within the fluid chamber;
• an aliquoting chamber;
• a fluid duct connecting the fluid chamber with the aliquoting chamber;
• a metering chamber;
• a connecting duct which fluidically connects the metering chamber with the aliquoting chamber, wherein the measurement structure is connected to the metering chamber via a third valve structure;
• and
• a vent connected to the metering chamber, wherein the vent is nearer to the rotational axis than the metering chamber;
• wherein the method comprises:
• placing the blood sample into the inlet;
• rotating the cartridge about the rotational axis to transport the blood sample into the blood separation chamber;
• controlling the rotation of the cartridge about the rotational axis to separate the blood plasma from corpuscular blood sample components by centrifugation;
• opening the first valve structure and rotating the cartridge about the rotational axis to transport a defined portion of the blood plasma from the blood separation chamber to the processing chamber;
• holding the portion of the blood plasma in the processing chamber, wherein the blood plasma mixes with the reagent and combines with the at least one specific binding partner to form the at least one analyte specific binding partner complex;
• releasing the seal to enable a first part of the washing buffer to enter the measurement structure, wherein the step of releasing the seal enables the washing buffer to enter the aliquoting chamber;
• controlling the rotational rate of the cartridge to permit the washing buffer in the aliquoting chamber to transfer into the connecting duct and to fill the metering chamber a first time;
• opening the second valve structure to transfer the at least one analyte specific binding partner complex to the measurement structure and controlling the rotational rate of the cartridge to allow the at least one analyte specific binding partner complex to flow to the measurement structure through the second valve structure;
• controlling the rotational rate of the cartridge to allow the at least one analyte specific binding partner complex to flow across the membrane to the absorbent structure at a defined velocity and to allow the at least one analyte specific binding partner complex to bind to the immobilized binding partner;
• controlling the rotational rate of the cartridge to transfer the first part of the washing buffer from the metering chamber through the valve into the measurement structure and to transfer a first remaining part back into the aliquoting chamber;
• controlling the rotational rate of the cartridge to allow the first part of the washing buffer to flow across the membrane to the absorbent structure at a defined velocity;
• controlling the rotational rate of the cartridge to allow the washing buffer in the aliquoting chamber to transfer into the connecting duct and to fill the metering chamber a second time;
• controlling the rotational rate of the cartridge to transfer a second part of the washing buffer from the metering chamber through the valve into the measurement structure and to transfer a second remaining part back into the aliquoting chamber;
• controlling the rotational rate of the cartridge to allow the second part of the washing buffer to flow across the membrane to the absorbent structure;
• and
• measuring the quantity of the analyte using the membrane and using an optical measurement system.