We have proposed an interferometric setup for biomedical analysis in transillumination modality. Wavelength dependence of optical properties must be considered for selecting source and sample. An expansion of the sample optical properties, around the central wavelength of emission, serves to account for spectral effects. Expected spectral values depend on the central moments of the source, and specific constants associated to the optical properties of the sample. By matching wavelength characteristics of source and sample, a first-order approximation is applicable. In such case, the expected values are exactly the optical properties evaluated at the central wavelength. Furthermore, in the first-order approximation, the transillumination interferometer yields the integrated attenuation of the sample at the central wavelength of emission. We verify the latter assertion by performing a wavelength-dependent Monte Carlo analysis to calculate the response of the transillumination interferometer. Recovered attenuation coefficients, for imaging and characterization scenarios, are in agreement with the value computed at the central wavelength of the source.