Why Different Brands Give Different Results

Different breath-testing devices can produce different readings even when measuring the same person at nearly the same time. The most important reasons are:

1. Different sensor technologies
   • MOS (metal oxide), electrochemical, infrared, and spectroscopic sensors behave differently.
   • They vary in sensitivity, selectivity, and susceptibility to interference.
2. Cross-sensitivity to other breath compounds
   • Breath contains acetone, ethanol, isoprene, methanol, hydrogen, and hundreds of other VOCs.
   • Devices differ in how well they distinguish acetone from other compounds.
3. Calibration differences
   • Different calibration gases, procedures, and intervals create systematic offsets.
4. Different breath sampling methods
   • Some devices measure the whole breath, others focus on end-tidal (alveolar) breath.
   • The measured acetone concentration increases throughout exhalation.
5. Humidity compensation
   • Breath is nearly 100% humid.
   • Devices handle water vapor differently.
6. Temperature compensation
   • Breath temperature, sensor temperature, and ambient temperature affect readings.
7. Proprietary algorithms
   • Manufacturers apply different filtering, smoothing, and conversion methods before displaying results.

How Much Breathing Technique Affects Results

Technique can have a very large impact, often larger than real metabolic changes.

Common effects:

Why Technique Matters

Acetone concentration rises during exhalation:

1. Mouth/throat air (lowest acetone)
2. Airway air
3. Deep alveolar air (highest acetone)

A short exhale samples less alveolar air and typically reports a lower value than a long, complete exhale.

Key Conclusion

For breath acetone measurements, the largest sources of disagreement are usually:

1. Sensor technology
2. Cross-sensitivity to other breath compounds
3. Breath sampling method
4. User breathing technique

A 2–5× difference between readings can result from breathing technique alone, even when the person's metabolic state remains unchanged. The most reliable way to track ketosis is to use the same device, follow the same breathing protocol, and focus on trends over time rather than absolute values.

To establish a consistent technique, take repeated measurements and refine your breathing method until consecutive readings are similar or nearly identical. Consistent results indicate that your technique is stable and that changes in readings are more likely to reflect actual metabolic changes.

References:

• PubMed - Volatile Organic Compounds in Human Breath
• PubMed - Breath Acetone Review
• PubMed - End-Tidal Breath Sampling