Validation of NoSAS (Neck, Obesity, Snoring, Age, Sex) score as a screening tool for obstructive sleep apnea: Analysis in a sleep clinic

Abstract

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.

Keywords: Diagnosis; NoSAS score; Obstructive sleep apnea; Prioritization; Screening.