1. A method of detecting a disease agent in a blood sample, the method comprising the steps of: (i) creating a sample infra-red spectrum representative of the blood sample, the sample spectrum having one or more spectral components, each component having a wavenumber and absorbance value. (ii) providing a reference database of spectral models, each model having one or more database spectral components of a wavenumber and an absorbance value, wherein the database spectral components identify disease agents, (iii) determining whether the reference database has one or more database spectral components corresponding to one or more sample spectral components, and (iv) compiling a list of corresponding database components identified.