Abstract: A method and system is described for rapidly classifying a sample of a biological fluid, comprising obtaining a spectrum of the biological fluid in response to excitation of the sample in a specified frequency range, and applying a multivariate classifier to one or more spectral regions of the spectrum to classify the biological sample into one class in a set of classes, the classes comprising at least two disease states having similar clinical symptoms. Methods and systems for developing the classifiers are also described. In one example the classification uses a vibrational spectrometer (5) to provide spectra from serum. The multivariate classifier may run on processor (9) to distinguish between disease states having similar clinical symptoms, such as malaria and cerebral malaria.