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Practice Management Issues Measurement of FeNO: The ATS and the ERS issued a statement in 2005 regarding equipment specifications and the standardization of procedures for the measurement of exhaled NO. The required specifications for NO analyzers are reproduced in Table 3. An example of the test procedure used at the Mayo Clinic Rochester is provided in Table 4. Various factors influencing FeNO are found in Table 1.  

Equipment: In the United States, only one device (NIOX; Aerocrine; Solna, Sweden) has received US Food and Drug Administration (FDA) approval for clinical use. A newer model (NIOX FLEX; Aero-crine) will be launched soon. These devices are targeted for academic centers and specialty clinics. A portable unit based on an electrochemical sensor and not chemiluminescence (NIOX MINO; Aerocrine) was introduced in Europe in 2005 but has not been approved by the FDA as of this writing. 

It is a hand-held device designed for use by specialists, general hospitals, primary care physicians, and patients. The FDA labeling restricts the operation of the NIOX device to trained physicians, respiratory therapists, nurses, and laboratory technicians. Both the NIOX FLEX and NIOX MINO devices allow results to be printed. None of the models have the Table 1—Required Specifications for NO Analyzers

 

Parameters	FeNO	Nasal NO
Sensitivity	1 ppb (noise, < 0.5 ppb)	10 ppb
Signal/noise ratio	> 3:1	Same as exhaled NO
Accuracy	> 1 ppb	> 10 ppb
Range	1-500 ppb	10-50 ppm
Instrument response timet	< 500 ms	< 500 ms
System lag timej	To be measured and reported by the investigator	Same as FeNO
Drift	< 1% of full scale/24 h	Same as FeNO
Reproducibility	> 1 ppb	> 10 ppb
Flow-through sensor	To be measured by manufacturer and reported in publications	Same as exhaled NO

Defined as the delay from the introduction of a square-wave signal until achievement of 90% of the maximum signal, inclusive of electronic delays and inherent instrument physical delays because of sample introduction, but not including tubing length.

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