An optical detection
assembly for monitoring a fluid includes a
light source, a
light detector array, and a controller. The controller receives signals from the
light detector array that are indicative of the intensity of light received by the
light detector array after the light has passed through the fluid. The controller generates a scattering profile based on the signals, with the scattering profile including rising and falling edges each having a slope. The controller calculates one or both slopes and determines the
platelet mass index (for a
platelet-containing fluid) and / or the concentration of a substance in the fluid based on said slope(s). The optical detection
assembly may also be used to analyze a reference fluid having a known concentration of the substance, with signals received by the controller when analyzing the reference fluid being a factor when determining the concentration of the substance in the fluid of interest.