***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background To evaluate the sensitivity , specificity and predictive values of fractional exhaled nitric oxide ( FENO ) for the diagnosis of asthma in general practice . Methods Prospect i ve diagnostic study with 160 patients attending 10 general practice s for the first time with complaints suspicious of obstructive airway disease ( OAD ) . Patients were referred to a lung function laboratory for diagnostic investigation . The index test was FENO measured with a portable FENO analyser based on electrochemical sensor . The reference st and ard was the Tiffeneau ratio ( FEV1/VC ) as received by spirometric manoeuvre and /or results of bronchial provocation . Bronchial provocation with methacholine was performed to determine bronchial hyper-responsiveness ( BHR ) in the event of inconclusive spirometric results . Results 88 ( 55 % ) were female ; their average age was 43.9 years . 75 ( 46.9 % ) patients had asthma , 25 ( 15.6 % ) had COPD , 8 ( 5.0 % ) had an overlap of COPD and asthma , and 52 ( 32.5 % ) had no OAD . At a cut-off level of 46 parts per billion ( ppb ) ( n = 30 ; 18.8 % ) , sensitivity was 32 % ( 95%CI 23–43 % ) , specificity 93 % ( 95%CI 85–97 % ) , positive predictive value ( PPV ) 80 % ( 95%CI 63–91 % ) , negative predictive value ( NPV ) 61 % ( 95%CI 52–69 % ) when compared with a 20 % fall in FEV1 from the baseline value ( PC20 ) after inhaling methacholine concentration ≤ 16 mg/ml . At 76 ppb ( n = 11 ; 6.9 % ) specificity was 100 % ( 95%CI 96–100 % ) and PPV was 100 % ( 95%CI 72–100 ) . At a cut-off level of 12 ppb ( n = 34 ; 21.3 % ) , sensitivity was 90 % ( 95%CI 79–95 % ) , specificity 25 % ( 95%CI 17–34 % ) , PPV 40 % ( 95%CI 32–50 ) , NPV 81 % ( 95%CI 64–91 % ) when compared with a 20 % fall of FEV1 after inhaling methacholine concentration ≤ 4 mg/ml . Three patients with unsuspicious spirometric results have to be tested with FENO to save one bronchial provocation test . Conclusion Asthma could be ruled in with FENO > 46 ppb . Mild and moderate to severe asthma could be ruled out with FENO ≤ 12 ppb . FENO measurement with an electrochemical sensor might be reasonable with respect to the time consuming procedure of bronchial provocation , which carries also some risk of severe bronchospasm . Further research is necessary to evaluate the effectiveness of this dual diagnostic strategy . The number needed to diagnose might be improved when the diagnostic precision could be enhanced by future technical developments BACKGROUND Assessing bronchial hyper-responsiveness ( BHR ) is a main diagnostic criterion of asthma .  Provocation testing is not readily available in general practice , but peak expiratory flow ( PEF ) is . Several guidelines promote the use of PEF variability as a diagnostic tool for BHR . This study tested the agreement between histamine challenge testing and PEF variability , and the consequences for diagnosing asthma . AIM To investigate the possibility of assessing BHR by PEF variability , using a histamine provocation test as a reference . METHOD Subjects with signs of symptoms indicating asthma ( persistent or recurrent respiratory symptoms or signs of reversible bronchial obstruction ) ( n = 323 ) were studied . They had been identified in a population screening for asthma . A histamine provocation test and PEF variability were assessed over a three-week period . Asthma was defined as signs or symptoms together with a reversible airflow obstruction or BHR to the histamine challenge test .  BHR was defined as a PC20 histamine of < or = 8 mg/ml or a PEF variability of > or = 15 % . Overall correlation between PC20 and PEF variability was calculated using Spearman 's rho . Furthermore , a decision tree was constructed to clarify the role of BHR in diagnosing asthma . RESULTS Thirty-two patients had a reversibility in forced expiratory volume in 1 second ( FEV1 ) of > or = 9 % predicted , 131 patients showed a PC20 of < or = 8 and 11 patients had a PEF variability of > or = 15 % . Overall correlation was poor at only -0.27 ( P < 0.0001 ) . One hundred and fourteen of the 131 patients diagnosed as having asthma when the histamine challenge test was used were not diagnosed by PEF variability . CONCLUSION PEF variability can not replace bronchial provocation testing in assessing BHR . This indicates that PEF variability and bronchial provocation do not measure the same aspects of BHR . If BHR testing is required in diagnosing asthma , a bronchial provocation test has to be used in general practice as well In athletes , exercise‐induced respiratory symptoms are common and their assessment is time and re source consuming . BACKGROUND Asthma diagnosis is based on the presence of symptoms and the demonstration of airflow variability . Airway inflammation measured by fractional exhaled nitric oxide , measured at a flow rate of 50 ml/s ( FE(NO50 ) ) remains a controversial diagnostic tool . AIM To assess the ability of FE(NO50 ) to identify bronchial hyperresponsiveness ( BHR ) to methacholine ( provocative concentration of methacholine causing a 20 % fall in FEV(1 ) ; PC20 M ≤ 16 mg/ml ) and to establish whether or not symptoms relate to FE(NO50 ) and PC20 M in patients with no demonstrated reversibility to β(2 ) -agonist . METHODS We conducted a prospect i ve study on 174 steroid naive patients with respiratory symptoms , forced expiratory volume in 1 s ( FEV(1 ) ) ≥ 70 % predicted and no demonstrated reversibility to β(2 ) -agonist . Patients answered to a st and ardised symptom question naire and underwent FE(NO50 ) and methacholine challenge . Receiver-operating characteristic ( ROC ) curve and logistic regression analysis assessed the relationship between PC20 M and FE(NO50 ) , taking into account covariates ( smoking , atopy , age , gender and FEV(1 ) ) . RESULTS A total of 82 patients had a PC20 M ≤ 16 mg/ml and had significantly higher FE(NO50 ) ( 19 ppb vs. 15 ppb ; p < 0.05 ) . By constructing ROC curve , we found that FE(NO50 ) cut-off value of 34 ppb was able to identify not only BHR with high specificity ( 95 % ) and positive predictive value ( 88 % ) but low sensitivity ( 35 % ) and negative predictive value ( 62 % ) . When combining all variables into the logistic model , FE(NO50 ) ( p = 0.0011 ) and FEV(1 ) ( p < 0.0001 ) were independent predictors of BHR whereas age , gender , smoking and atopy had no influence . The presence of diurnal and nocturnal wheezing was associated with raised FE(NO50 ) ( p < 0.001 and p < 0.05 , respectively ) . CONCLUSION The value of FE(NO50 ) > 34 ppb has high predictive value of PC20 M < 16 in patients with suspected asthma in whom bronchodilating test failed to demonstrate reversibility or was not indicated . However , FE(NO50 ) ≤ 34 ppb does not rule out BHR and should prompt the clinician to ask for a methacholine challenge INTRODUCTION Exercise-induced bronchoconstriction ( EIB ) is present in 40 to 90 % of patients with asthma .  Exhaled NO ( eNO ) levels have been correlated with bronchial hyperresponsiveness to methacholine , and have correlated with the degree of decrease in FEV(1 ) with exercise . The purpose of our study was to examine whether eNO measurements prior to or after exercise could be used as a surrogate marker of exertional bronchoconstriction in a population referred specifically for the evaluation of EIB . METHODS We studied 50 consecutive subjects without a history of asthma who were referred for the clinical evaluation of EIB .  eNO levels were measured prior to exercise challenge and every 5 min for a total of 30 min after exercise . Forced expiratory flows were measured prior to and serially after exercise challenge . RESULTS Seven subjects had a decrease in FEV(1 ) of > or = 15 % with exercise . The mean eNO level prior to exercise was 41 parts per billion ( ppb ) [ median + /- SD , 23 + /- 42.2 ppb ] in the EIB group and 25.6 ppb ( median , 19.95 + /- 18.47 ppb ) in the group without EIB . A receiver operator characteristic curve yielded a value of 0.636 . When using an eNO level of < 12 ppb , the sensitivity , specificity , negative predictive value , and positive predictive value for EIB were 1.0 , 0.31 , 0.19 , and 1.0 , respectively ; therefore , no one with a baseline eNO of < 12 ppb demonstrated EIB . CONCLUSIONS No subjects with very low pre-exercise eNO levels ( < 12 ppb ) demonstrated bronchial hyperresponsiveness to exercise . eNO measurement may obviate the need for bronchoprovocation testing in patients who complain of exertional dyspnea BACKGROUND Whole-body plethysmography ( WBP ) with bronchial challenge testing to measure the ( specific ) airway resistance , (s)R(AW ) , is considered to be a more sensitive diagnostic procedure than spirometry , which can only measure the forced expiratory volume in one second ( FEV1 ) . The evidence for the added diagnostic value of WBP is not yet conclusive . METHODS In a prospect i ve diagnostic study , we carried out WBP with bronchial challenge testing as well as a bronchodilation test in 400 patients with suspected asthma from June 2010 to October 2011 . The bronchial provocation test was considered positive if the FEV1 fell by at least 20 % and /or the airway resistance doubled , with an increase of the sR(AW ) to at least 2.0 kPA × s and /or of the R(AW ) to 0.5 kPA × s/L. Follow-up evaluation was performed one year later . RESULTS The prevalence of asthma in the 302 patients who completed follow-up was 27.5 % .  The sensitivity of WBP with sR(AW ) measurement for asthma was 95.2 % ( 95 % confidence interval [ CI ] 88.3%-98.1 % ) , and its specificity was 81.7 % ( 95 % CI 76.1%-86.3 % ) . The sensitivity of FEV1 was 44.6 % ( 95 % CI 34.4%-55.3 % ) , and its specificity was 91.3 % ( 95 % CI 86.6%-94.4 % ) . The negative predictive value ( NPV ) of WBP with sR(AW ) measurement was 97.8 % ( 95 % CI 94.5%-99.1 % ) , while that of FEV1 was 81.3 % ( 95 % CI 76.0%-85.7 % ) . The positive predictive value ( PPV ) of WBP with sR(AW ) measurement was 66.4 % ( 95 % CI 57.5%-74.2 % ) , while that of FEV1 was 66.1 % ( 95 % CI 53.0%-77.1 % ) . CONCLUSION With sR(AW ) measurement , asthma can be ruled out with high certainty . Improving the positive predictive value of testing for asthma remains a challenge , however , as sR(AW ) measurement does not yield any increase in specificity BACKGROUND The fraction of exhaled NO ( FeNO ) is valuable for the follow-up of asthmatic patients . However , its usefulness as a screening tool for asthma is not established . METHODS We screened a population of 961 university students with a modified European Community Respiratory Health Survey question naire that has been previously used for the screening of respiratory symptoms related to asthma . All subjects with a positive answer to at least one question ( n = 149 ) were su bmi tted to FeNO measurement with a portable nitric oxide analyzer . Subsequently , they were su bmi tted to spirometry and evaluated by a physician blinded to FeNO measurements . Seventy students with no respiratory symptoms served as control subjects . RESULTS Asthma was diagnosed in 63 subjects , and allergic rhinitis was diagnosed in 57 subjects . Asthmatics presented higher FeNO values than control subjects ( median , 20 parts per billion [ ppb ] ; interquartile range , 14 to 31 ppb ; vs median , 11 ppb ; interquartile range , 7 to 13 ppb , respectively ; p < 0.0001 ) , whereas they did not differ from patients with allergic rhinitis ( median , 1 
    Output:
    
Conclusions There appears to be a fair accuracy of FENO for making the diagnosis of asthma .
The overall specificity was higher than sensitivity , which indicates a higher diagnostic potential for ruling in than for ruling out the diagnosis of asthma