A method and apparatus for characterizing the type of a blood sample and a variety of blood components are provided wherein a transmission spectrum of the sample is collected over a predetermined wavelength range. For blood typing, this spectrum is then compared with a set of control spectra collected from control blood samples having known blood types, from which the type of the blood sample can be determined. Further methods and apparatus are provided for determining the viability of and for cross matching a platelet unit. Additional method and apparatus permit analysis of the sample for the presence of a contaminant. Particles can also be counted in the sample, even when present in low concentrations, including white blood cell.