Method and system for determining plasma protein content of whole blood using refractometry

A system for measuring component content of a fluid sample, the system comprising:

• a light source;
• a light sensor;
• a container including a prism having a sensing surface;
• a support member configured to hold the container relative to the light source and the light sensor such that light generated by the light source reflects off the sensing surface to the light sensor;
• a controller configured to:
• calibrate the system by identifying a calibration pixel pattern of first pixels of the light sensor illuminated by light from the light source that has reflected off the sensing surface when a reference fluid is present in the container supported by the support member, the reference fluid having a known reference density;
• identify a sample pixel pattern of second pixels of the light sensor illuminated by light from the light source that has reflected off the sensing surface when the fluid sample is present in the container;
• identify a pixel shift distance along the light sensor from the calibration pixel pattern to the sample pixel pattern, the pixel shift distance measured between the first pixels and the second pixels having a common brightness;
• and
• determine the component content of the fluid sample based on the pixel shift distance multiplied by K, the product of which is added to C,
• wherein:
• K is an experimentally derived proportionality constant specific to at least one of prism material of the prism, wavelength of the light source, resolution of the light sensor, and an optical geometry of the prism;
• and
• C is a simulated plasma protein concentration value of the reference fluid.

An apheresis system comprising:

• an apheresis machine configured to separate a fluid component from a fluid sample;
• a refractometer configured to measure component content of the fluid sample, the refractometer including:
• a light source;
• a light sensor;
• a cuvette including a prism with a sensing surface;
• and
• a support member configured to hold the cuvette relative to the light source and the light sensor such that light generated by the light source reflects off the sensing surface to the light sensor;
• and
• a controller configured to:
• calibrate the refractometer by identifying a calibration pixel pattern of first pixels of the light sensor illuminated by light from the light source that has reflected off the sensing surface while a reference fluid is present in the cuvette supported by the support member, the reference fluid having a known reference density;
• identify a sample pixel pattern of second pixels of the light sensor illuminated by light from the light source that has reflected off the sensing surface while the fluid sample is present in the cuvette;
• identify a pixel shift distance along the light sensor from the calibration pixel pattern to the sample pixel pattern, the pixel shift distance measured between the first pixels and the second pixels having a common brightness;
• determine the component content of the fluid sample based on the pixel shift distance multiplied by K, the product of which is added to C;
• and
• activate the apheresis machine to separate the fluid component from the fluid sample when the component content that is determined is within a predetermined range,
• wherein:
• K is an experimentally derived proportionality constant specific to at least one of prism material of the refractometer, wavelength of the light source, resolution of the light sensor, and an optical geometry of the refractometer;
• and
• C is a simulated plasma protein concentration value of the reference fluid.