obstructive sleep apnea ( osa ) is a common public health problem worldwide and it has been shown to be associated with an increased incidence of cardiovascular complications such as death , stroke , or myocardial infarction . the 2014 american heart association / american stroke association guideline recommends that patients with stroke / transient ischemic disorder ( tia ) showed be worked up for osa . in this study , patients who had osa and stroke had an improved outcome with continuous positive airway pressure . extrapolating data from western population and implementing in the asian populations may not be possible as there are differences in genetic and anatomical factors . for example , the cutoff point for obesity based on body mass index ( bmi ) criterion for western population is 30 kg / m meanwhile the bmi for asian population is 25 kg / m . it is also evident that there are differences in anatomical factors between asian and caucasian population such as retrognathia and oropharyngeal width which are main risk factors for osa . alternatively , the stop - bang questionnaire developed by chung et al . has been widely used as a sensitive screening tool for osa . the stop - bang acronym stands for : snoring history , tired during the day , observed stop breathing while sleep , high blood pressure , bmi more than 35 kg / m , age more than 50 years , neck circumference more than 40 cm and male gender . the authors recommended that if a patient had 3 or more criteria mentioned above , it is strongly suggestive for osa . however , the cut - off values of this questionnaire are based on the data from caucasians , therefore we hypothesized that to use it in asian population , some adjustments are needed . we compared the clinical features in the stop - bang questionnaire between osa - induced hypertension patients and healthy control subjects . the study was conducted in the faculty of medicine , khon kaen university ( thailand ) . the study protocol was approved by the ethics committee for human research , khon kaen university . osa induced - hypertension patients were diagnosed by : i ) met the criteria of hypertension ; ii ) having average apnea - hypopnea index ( ahi ) by polysomnography more than or equal 5 times / hours and iii ) no evidence of other secondary hypertension . the control subjects filled up the modified berlin questionnaire and epworth sleepiness scale less than 10 and defined as low risk for osa with low scores . demographic data and clinical features of both osa - induced hypertension patients and healthy subjects were recorded and compared . the clinical features included age , gender , bmi , neck circumference , mallampati classification , torus palatinus , and torus mandibularis . the mallampati classification was defined by asking the subjects to protrude their tongue as much as possible and classified as class 1 to 4 . the sample size of the study population was calculated by using the proportion comparison between osa and healthy subjects using winpepi program . the proportion of osa was 0.35 and the healthy control was 0.07 with deviation of 5% , power of 90% , and missing data of 10% . the sample size was calculated to be 102 subjects ( osa 34 subjects and healthy control 68 subjects ) . due to the incompleteness of the database of medical students , 120 healthy controls were selected by systematic sampling from the database ( total of 1174 medical students ) . baseline and clinical characteristics of the participants in both groups were compared using descriptive statistics . univariate logistic regression analyses were applied to calculate the crude odds ratios of individual variables for having osa . all clinically significant variables or p<0.20 by the univariate analyses were included in subsequent multivariate logistic regression analyses . analytical results were presented as crude odds ratios ( or ) , adjusted or , and 95% confidence intervals ( ci ) . significant risk factors were calculated for the best cut - off points by the receiver operator characteristic curve ( roc curve ) . data analyses were performed with stata software ( college station , tx , usa ) and spss software ( chicago , il , usa ) . in this study , 42 osa - induced hypertension patients and 82 control subjects who had a complete set of clinical data were included . all clinical features of both groups the osa - induced hypertension patients were significantly older ( 59.5 vs 21.0 years ) , with higher proportion of males ( 64.3 vs 59.8% ) , more obese ( 78.6 vs 6.1% ) , higher incidence of mallampati class 3 or more ( 54.8 vs 24.4% ) , larger neck circumference ( 41.3 vs 32.0 cm ) , higher incidence of torus palatinus ( 26.6 vs 0% ) and of torus mandibularis ( 9.5 vs 0% ) . by multiple logistic regression analysis , only two factors bmi and neck circumference , the adjusted odds ratios for both factors were 1.49 ( 95% ci : 1.06 , 2.09 ) and 1.67 ( 95% ci : 1.11 , 2.51 ) , respectively . by the roc curve analyses , the best cut - off points for the bmi and the neck circumference were 24.5 kg / m ( figure 1a ) and 36 cm ( figure 1b ) . the sensitivity and the specificity for bmi cut - off point were 97.2% and 91.4% , whereas those for the neck circumference were 94.7% and 82.9% . the present results showed that the stop - bang questionnaire needed to adjust the cutoff values of the bmi and neck circumference suitable for thai population . subjects should referred for polysomnography if positive at least 3 questions : s , snoring history ; t , tired during the day ; o , observed stop breathing while sleep ; h , high blood pressure ; b , bmi more than 25 kg / m ; a , age more than 50 years ; n , neck circumference more than 36 cm ; g , male gender ( modified from chung et al . ) . for the criteria of obesity for asians , the cut - off of the bmi should lower from 35 kg / m to 24.5 or round up to 25 kg / m . the cut - off of the neck circumference also should be lowered from 40 cm to 36 cm for asians . proposed the cutoff points of 24.1 kg / m for the bmi and 35.5 cm for the neck circumference for japanese population . using stop - bang questionnaire is very suitable for thailand and other developing countries due to limited availability of polysomnography , the standard diagnostic tool for osa . this low cost tool can select appropriate patients for referral to sleep center for further polysomnography . healthy control subjects were not performed polysomnography to exclude osa . however , both the berlin questionnaire and the epworth sleepiness scale were used to exclude osa , which has a sensitivity and specificity of 0.86 , 0.95 and 0.49 , 0.80 , respectively . even though the age is a significant factor by univariate logistic regression , it was not included in the subsequent multivariate regression . this is because the difference of age group composition between the osa and the healthy control subjects . further studies , therefore , are needed to confirm the results of this study and to identify the appropriate cut - off point using the age- and sex - matched controls . also , to increase their sensitivity and specificity , osa patients with other complications than hypertension should be included and compared . whether simple measurement of the neck circumference and the bmi calculation are sufficient to identify osa patients in routine practice by primary health care personnel including physicians , nurses and volunteers should be examined in further study . osa has been proved to be a contributing factor for major cardiovascular diseases ; stroke , hypertension , sudden death , and also coronary artery disease . treatment of osa may reduce large economic burden from prevention of the morbidity and mortality from stroke and acute coronary syndrome . in conclusion , the appropriate cut - off points for the bmi and the neck circumference for stop - bang questionnaire were 25 kg / m and 36 cm for asian people . all hypertensive patients should have their bmi and neck circumference measured to detect the risk factors for osa . public health campaign for osa screening is also needed to reduce morbidity and mortality from osa complications .
obstructive sleep apnea ( osa ) is a common public health issue . if left untreated , osa may cause a large health economic burden from cardiovascular complications particularly stroke . 
 the diagnosis of osa can be made by polysomnography , but its availability is limited in the developing countries in asia . 
 stop - bang questionnaire is a good screening tool but may need some adjustment for asian population . 
 stop - bang stands for : snoring history , tired during the day , observed stop breathing while sleep , high blood pressure , body mass index ( bmi ) more than 35 kg / m2 , age more than 50 years , neck circumference more than 40 cm and male gender . 
 we compared clinical features in stop - bang questionnaire between 42 osa induced hypertension patients and 82 healthy control subjects in the faculty of medicine , khon kaen university , thailand . 
 the best cutoff point for the bmi and the neck circumference were 24.5 kg / m2 and 36 cm , respectively . 
 the sensitivity and specificity of the bmi cutoff point were 97.2% and 91.40 , while those of the neck circumference were 94.7% and 82.9% . in conclusion , the appropriate cutoff points of bmi and neck circumference for thai stop - bang questionnaire were 25 kg / m2 and 36 cm .