A method of measuring whole-blood hemoglobin parameters includes providing a LED light source, guiding light having the spectral range from the LED light source along an optical path, providing a cuvette module with a sample receiving chamber, providing a pair of first and second optical diffusers disposed in the optical path where the cuvette module is disposed between the pair of first and second optical diffusers, guiding light from the cuvette module into an optical spectrometer, and processing an electrical signal from the spectrometer into an output signal useable for displaying and reporting hemoglobin parameter values and/or total bilirubin parameter values of the sample of whole blood.