Breath test apparatus and methods

A breath test method, comprising the steps of:

• performing a first measurement of the isotopic ratio of at least a first breath sample of a subject;
• performing a second measurement of the isotopic ratio of at least a second breath sample of said subject;
• and
• determining when said second measurement shows sufficient deviation from said first measurement that a clinically significant result of the breath test may be concluded;
• wherein the level of said sufficient deviation is allowed to undergo variation during said breath test.

A breath test method for determining the presence of a clinically significant state in a subject, comprising the steps of:

• performing measurements of the changes from a baseline of an isotopic ratio in a plurality of samples of exhaled breath of said subject, following the effective cessation of oral activity;
• determining a polynomial which approximates the functional plot of said measurements with time;
• calculating a weighted standard deviation of said measurements from said polynomial, wherein for measurements over said baseline by more than a predetermined amount, a predefined fractional part of the measurement is taken, while for measurements not over said baseline by more than said predetermined amount, the measurement is taken in its entirety;
• and determining whether said weighted standard deviation exceeds a predetermined level.

A breath test method comprising the steps of:

• performing a measurement of the isotopic ratio of at least a first breath sample of a subject;
• and
• determining when said measurement shows sufficient deviation from a baseline measurement that a clinically significant result of the breath test may be concluded;
• wherein said deviation comprises an upper and a lower threshold band of uncertainty, and wherein the extent of this band is dependent on at least one of the parameters selected from the group consisting of the elapsed time of said breath test, the standard deviation of the physiological spread of results, the dynamics of the physiological change in isotopic ratio, the number of points measured in the breath test, the environmental conditions present during the breath test, and the noise and/or drift levels of the instrument executing the breath test.

A method for determining the reliability of a breath test, comprising the steps of:

• obtaining results from said breath test;
• defining a reliability parameter by combining at least one of the criteria selected from the group consisting of the instrument noise and/or drift level, the standard deviation of the physiological spread of results, the dynamics of the physiological change in isotopic ratio, and the time elapsed since ingestion of a labeled substrate;
• and
• using said reliability parameter to assess the results of said breath test according to a predetermined reliability criterion.

A breath test instrument comprising:

• tubing for collecting breath from a subject;
• and
• a gas analyzer for determining isotopic ratio in said gas;
• wherein said gas analyzer monitors changes in an isotopic ratio of a gas in exhaled breath samples of said subject virtually continuously, and determines that said test has a clinically significant outcome in accordance with the ongoing results of said test.