The present teachings describe a method for testing a biological sample, including (a) obtaining a biological sample from a mammal, (b) acquiring at least two extracellular endogenous metabolic products from the biological sample, (c) detecting the at least two extracellular endogenous metabolic products from the extract, (d) determining a pattern on the basis of the presence or the mass ratio of the at least two extracellular endogenous metabolic products, (e) comparing the pattern with the pattern from a retention sample.