A method for extending an effective working range of an analyzer for measuring an analyte in a breath sample. The method includes initiating a reaction in the analyzer that produces an optically discernable reaction product having an optical property that is indicative of a concentration of the analyte in the breath sample, taking a first reading of the optical property at a first time, and comparing the first reading to a reference. If the comparison yields a first state, the method includes determining the concentration using the first reading. If it yields a second state different from the first state, the method includes taking a second reading of the optical property at a second time, and determining the concentration of the analyte using the second reading. Other methods are provided as well.