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From:
Am J Respir Crit Care Med. Author manuscript; available in PMC 2014 April 21.
Published in final edited form as:
Am J Respir Crit Care Med. 2008 August 1; 178(3): 218–224.
Published online 2008 May 14. doi: 10.1164/rccm.200711-1754OC

TABLE 2

Clusters in Primary Care
Cluster 1
Cluster 2
Cluster 3
VariablePrimary Care
(n = 184)
Early-Onset Atopic Asthma
(n = 61)
Obese Noneosinophilic
(n = 27)
Benign Asthma
(n = 96)
Significance
(P Value)*
Sex, % female 54.4 45.981.552.10.006
Age, yr (SD) 49.2 (13.9) 44.5 (14.3)53.9 (14)50.8 (13)0.003
Age of onset, yr (SD) 24.7 (19) 14.6 (15.4)35.3 (19.6)28.2 (18.3)<0.001
Atopic status, % positive 72.8 95.151.964.6<0.001
Body mass index, kg/m2 (SD) 27.5 (5.4) 26.1 (3.8)36.2 (5.5)26 (3.6)<0.001
PC20 methacholine, mg/ml 1.04 (1.13) 0.12 (0.86)1.60 (0.93)6.39 (0.75)<0.001
PC20 >8 mg/ml, n (%) 64 (34.7) 2 (3.3)6 (22.2)56 (58.3)<0.001
Peak flow variability, amp % mean 17 (0.38) 20 (0.47)21.9 (0.32)14.8 (0.32)0.039
FEV1 change with bronchodilator, % 1.63 (1.16) 4.5 (0.91)1.82 (1.16)0.83 (1.22)<0.001
Post-bronchodilator FEV1, % predicted 91.4 (21) 86.9 (20.7)91.5 (21.4)94.2 (20.7)0.107
Sputum eosinophil count, % 1.32 (0.62) 3.75 (0.64)1.55 (0.51)0.65 (0.44)<0.001
FeNO§, ppb 31.6 (0.33) 57.5 (0.27)25.8 (0.29)22.8 (0.27)<0.001
Sputum neutrophil count, % 55.09 (0.31) 45.87 (0.24)72.71 (0.13)57.56 (0.36)0.038
Modified JACS (SD) 1.36 (0.74) 1.54 (0.58)2.06 (0.73)1.04 (0.66)<0.001
Dose of inhaled corticosteroid, BDP equivalent/μg (SD) 632 (579) 548 (559)746 (611)653 (581)0.202
Long-acting bronchodilator use, % 40.2 34.448.241.70.442
Previous hospital admission or emergency attendance, no. per patient 0.60 (1.57) 1.040.260.200.037
Previous outpatient attendance, % attended 15% 22%19%6%0.121
Severe asthma exacerbations (requiring oral corticosteroids) in past 12 mo, no. per patient 1.25 (1.94) 1.86 (0.32)1.07 (0.32)0.39 (0.18)0.002

For definition of abbreviations, see Table 1.

Boldface type denotes population statistics. The column headed “Cluster 3” represents a cluster not observed in the secondary-care asthma population.

*Comparison between clusters using analysis of variance for continuous variables and χ2 test for proportions. Significance values for variables included in the cluster analysis are a product of the cluster algorithm and are provided for illustrative purposes only.
Variables included in the cluster analysis.
Geometric mean (log10 SD)
§Measured with NIOX at a flow rate of 50 ml/second.