A method of diagnosing the health of an individual by collecting a breath
sample from the individual and measuring the amount of each of a
plurality of analytes in the sample. The amount of each analytes is
measured by fitting a time response curve of a sample-evaluation fuel
cell in which the fuel cell sample electrode is contacted with the sample
with the analysis based on a function of standard time response curves
for an equivalent fuel cell configuration obtained separately for each of
the analytes on a fuel cell with equivalent construction as
sample-evaluation fuel cell. Each of the plurality of analytes is
generally indicative of an aspect of the individual's health. Suitable
analytes include, for example, inorganic compounds as well as
compositions that exhibit negative reduction reactions at least for a
portion of the time response curve. In particular, acetone exhibits a
negative potential/current peak when it is an analyte in a fuel cell in
an sample electrode with a counter electrode exposed to oxygen, which may
or may not be introduced in the form of air. Various forms of analysis to
estimate acetone concentrations in the breath can be used.