INTRODUCTION: Screening methods have become increasingly important due to the 
growing number of patients suspected of having obstructive sleep apnea (OSA) 
being referred to sleep clinics. The Lausanne NoSAS (Neck circumference, 
Obesity, Snoring, Age, Sex) score test is a simple, efficient, and easily 
employed tool enabling identification of individuals at risk for the disease. 
The score ranges from 0 to 17 and the patient has a high probability of OSA if 
they have a NoSAS score of 8 or higher.
OBJECTIVES: To evaluate the performance of the NoSAS score as a screening tool 
for the diagnosis of OSA in a sleep clinic.
METHODS: Prospectively, for 12 months, we included all the patients referred by 
primary care physicians to our sleep unit for clinical evaluation who had 
undergone in-lab polysomnography (PSG) and completed the NoSAS score. This test 
assigns 4 points for a neck circumference of more than 40cm, 3 points for a 
body-mass index of 25kg/m2 to less than 30kg/m2 or 5 points for having a 
body-mass index of 30kg/m2 or more, 2 points for snoring, 4 points for being 
older than 55 years of age and 2 points for being male.
RESULTS: Of the 294 patients, 70.7% were male, aged 53.5±12.1 years, with a neck 
circumference of 41.0±3.6cm and a BMI of 30.8±5.1kg/m2. OSA was present in 84.0% 
of the patients, 34.8% with moderate OSA and 36.4% severe OSA. Using the NoSAS 
model for the prediction of all OSA, moderate/severe OSA and severe OSA, the 
area under the ROC (Receiver Operating Characteristic) was 0.770 (IC95%: (0.703; 
0.837), p<0.001), 0.746 (IC95%: (0.691; 0.802), p<0.001) and 0.686 (IC95%: 
(0.622; 0.749), p<0.001), respectively, thus confirming the diagnostic ability 
of the NoSAS model. With a NoSAS score ≥7, the sensitivity and positive 
predictive value (PPV) were 94.3% and 87.6% for all OSA, 94.9% and 62.8% for 
moderate/severe OSA and 100% and 33.8% for severe OSA, respectively. With the 
same cut-off, the negative predictive value (NPV) for moderate/severe and severe 
OSA were 67.9% and 100%, respectively. Each increase in the NoSAS score was 
associated with an increase in the probability of OSA, reaching a 97% OSA 
probability for a score of 17.
CONCLUSIONS: The NoSAS score showed high sensitivity and PPV for OSA with 
specificity and diagnostic accuracy steadily increasing with higher scores. 
Furthermore, a low score showed high predictive value for the exclusion of 
moderate/severe OSA. Overall, our results suggest that, in primary care, this 
score can be a powerful tool for stratifying and prioritizing patients in the 
diagnosis of OSA. Nevertheless, more studies are needed to evaluate the efficacy 
of this score in hospital health care, in younger populations, with a 
predominance of female and non-obese individuals or in cardiovascular disease.