System and method of measuring hematocrit

A system for measuring hematocrit in a whole blood sample deposited on an absorbent substrate, the system comprising:

• a. at least one light source positioned to illuminate the blood sample on the substrate at first and second wavelengths, the first and second wavelengths being different from each other and falling in the range of 400 nm to 700 nm;
• b. a spectral sensor positioned to measure a first intensity and a second intensity of light diffusely reflected from the blood sample at the first and second wavelengths, respectively, wherein the diffusely reflected first and second intensities of light are compared to reference values to generate first and second reflectance values;
• and
• c. a controller, coupled to the spectral sensor, configured to (i) calculate first and second reflectances from the measured first and second intensities of diffusely reflected light by comparing the first and second intensities to reference values, (ii) determine a first differential reflectance between the first and second reflectances, and (iii) determine the hematocrit level of the whole blood sample based on a first stored relationship between hematocrit level and first differential reflectance corresponding to the first and second wavelengths.