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ORIGINAL RESEARCHVariability of FeNO in healthy subjects at 2240 meters above sealevelLaura Gochicoa-Rangel 1 • Ferm? ´n Rojas-Cisneros 1 • Jose ´ Luis Miguel-Reyes 2 •Selene Guerrero-Zu´n˜iga 1 • Uri Mora-Romero 1 • Ana Karen Maldonado-Mortera 1 •Luis Torre-Bouscoulet 1Received: 12 March 2015/Accepted: 8 July 2015? Springer Science+Business Media New York 2015Abstract Fraction of exhaled nitric oxide (FeNO) is amarker of eosinophilic airway inf l ammation. Altitudeabove sea level can affect measurements of this index, butthere is only limited information regarding the diurnalvariation (ante meridiem vs. post meridiem) and repro-ducibility of FeNO on consecutive days at moderate alti-tudes. To evaluate the diurnal variability of FeNO andassess its reproducibility over f i ve consecutive days inhealthy individuals living at 2240 m, and to compare theFeNO readings taken with two different analyzers. Healthynon-smoking adults were measured using NIOX MINO ? orNOA 280i ? devices. One group (n = 10) had readingstaken morning and afternoon for f i ve consecutive days withthe NIOX MINO ? equipment; while the second group(n = 17) was measured on only one morning but by boththe electrochemical analyzer (NIOX MINO ? ) and thechemiluminescence method (NOA 280i ? ). The study groupconsisted of 27 subjects aged 28.7 ± 6 years. Morning andafternoon FeNO measurements were 15.2 ± 7.5 ppb and15.2 ± 7.9 ppb (p = 0.9), respectively. The coeff i cient ofvariation (CV) of these measurements (a.m. vs. p.m.) was10.7 %, and the coeff i cient of repeatability (CR), 4.2 ppb.The concordance correlation coeff i cient (CCC) betweenthe two measures (morning vs. afternoon) was 0.91. TheCV and CR of the f i ve morning readings were 15.4 % and4.3 ppb, respectively; while those of the f i ve afternoonmeasures were 13.6 % and 3.5 ppb, respectively. The CCCbetween the NIOX MINO ? equipment and the NOA-280i ?device was 0.8, with 95 % limits of agreement of -8.35 to0.29 ppb. In adults living at 2240 m above sea level, FeNOmeasurements show minimal diurnal variation, and read-ings are reproducible (\15 %) over a period of at least f i veconsecutive days; however, the FeNO measurementsobtained with the NIOX MINO ? and NOA 280i ? devicesare not interchangeable due to the wide limits of agreementrecorded.Keywords Exhaled nitric oxide ? Circadian variation ?Cut-off points ? Electrochemical analyzer ?Chemiluminescence1 IntroductionFraction of exhaled nitric oxide (FeNO) is a marker ofeosinophilic airway inf l ammation. Its principal clinicalapplications are: (1) to establish diagnoses of eosinophilicasthma; and, (2) to predict responses and adherence totreatment with inhaled corticosteroids [1–3]. Also, mea-suring FeNO has proven to be useful for differentialdiagnoses in patients with chronic obstructive pulmonarydisease (COPD), cystic f i brosis, and ciliary dyskinesia [1].Our Center is a national-level referral hospital forpatients with respiratory diseases, located in Mexico City at2240 m above sea level. The principal reason for referringpatients to our institute is asthma, as we receive 1560 newcases per year with approximately 3900 patients seen in theemergency department. Since the altitude of Mexico Citycan affect measurements, and because informationregarding diurnal variation (i.e., ante meridiem vs. post& Luis Torre-Bouscouletluistorreb@gmail.com1Departamento de Fisiolog? ´a Respiratoria, Instituto Nacionalde Enfermedades Respiratorias ‘‘Ismael Cos? ´o Villegas’’,Calzada de Tlalpan 4502, Colonia Seccio´n XVI, Tlalpan,C.P. 14080 Mexico City, Distrito Federal, Mexico2Cl? ´nica de Asma, Instituto Nacional de EnfermedadesRespiratorias ‘‘Ismael Cos? ´o Villegas’’, Mexico City, Mexico123J Clin Monit ComputDOI 10.1007/s10877-015-9737-0