Storage conditions for stability of offline measurement of fractional exhaled nitric oxide after collection for epidemiologic research

Table 2 Changes in FeNO levels in Mylar bags stored at 4°C after sampling, in relation to various factors

	n	9 hours			24 hours			72 hours			168 hours
		%	(SD)	p value	%	(SD)	p value	%	(SD)	p value	%	(SD)	p value
Sex
Male	22	101.2	(9.0)	0.105	100.3	(10.8)	0.643	101.7	(16.3)	0.799	104.9	(29.8)	0.689
Female	26	97.9	(4.8)		99.2	(3.6)		102.7	(8.5)		107.7	(17.1)
Age (years)
<40	20	98.8	(4.0)	0.623	99.3	(4.7)	0.779	101.2	(7.5)	0.646	104.7	(15.0)	0.676
≥40	28	99.8	(8.8)		100.0	(9.4)		103.0	(15.2)		107.6	(28.3)
Wheezing
Yes	8	100.3	(4.0)	0.709	97.3	(4.4)	0.340	96.4	(10.0)	0.150	95.5	(22.5)	0.154
No	40	99.2	(7.7)		100.2	(8.2)		103.4	(12.7)		108.6	(23.4)
Allergic rhinitis or pollinosis
Yes	20	100.3	(8.7)	0.291	100.3	(9.6)	0.558	103.9	(15.5)	0.292	109.3	(28.9)	0.310
No	28	98.1	(4.1)		98.9	(4.0)		100.0	(6.0)		102.3	(12.4)
Cigarette Smoking
Never	33	98.5	(4.5)	0.010	99.3	(3.9)	0.007	101.6	(8.2)	0.003	105.2	(17.1)	0.006
Ever	9	97.5	(2.3)		95.7	(3.0)		95.1	(7.7)		93.9	(15.4)
Current	6	107.4	(15.9)* ^†		107.9	(18.4) * ^‡		116.4	(24.7) * ^‡		131.8	(43.5) * ^‡

Data are shown as percentages relative to the baseline values immediately after sampling.
* p<0.05, significantly different from nonsmokers. ^†p<0.05; ^‡p<0.01, significantly different from ex-smokers.

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