Introduction- Obstructive Sleep Apnoea (OSA) is a prevalent but frequently underdiagnosed disorder that can lead to significant medical repercussions if not identified promptly. This circumstance has necessitated the development of a preliminary, alternative diagnostic instrument for the early detection and severity evaluation of OSA.The objective of this study was to ascertain the correlation and concordance between the other screening questionnaire (like AHI, ESS and STOP bang) and the Oxygen Desaturation Index (ODI) in evaluating the severity of obstructive sleep apnoea (OSA). Material and methods- The present cross-sectional study was conducted for among patients of Obstructive sleep apnoea for a period of one year at a tertiary care centre. Through convenience sampling technique a total of 200 patients diagnosed with OSA through polysomnography (PSG) were taken for the study. Assessments of subjective sleepiness as determined sleep study metrics including the AHI, ESS and STOP bang and Oxygen Desaturation Index. Results- The patients BMI varied from 18.8 to 44.3, with a mean of 27.3±2.1. Forty six patients (23%) were classified as normal weight, whereas 116 patients (58%) were overweight, and 38 patients (19%) were categorised as obese.The study group exhibited an ESS ranging from 0 to 24, with a mean of 11.23±2.7. The average lowest SpO2 value was 73.5±3.6. The mean SpO2 value during PSG averaged 89.20±4.2.The Apnea-Hypopnea Index (AHI) ranged from 6 to 97, with a mean of 41.33±3.6. The mean Oxygen Desaturation Index (ODI) for the study group was 40.41±2.7, with values ranging from 4.8 to 96.2.In a Cohen’s weighted Kappa analysis, the Kappa and the proportional agreement observed between AHI and ODI in classifying severity of OSA was 0.66 and 87.12%. ODI>15 exhibited 100% sensitivity, 54.7% specificity, a positive predictive value (PPV) of 78%, and a negative predictive value (NPV) of 100%. The sensitivity for identifying patients with severe obstructive sleep apnoea (OSA) was 96.7% at an oxygen desaturation index (ODI) of 20 and 88.9% at an ODI of 25.There was a statistically significant relationship between ESS and mean SpO2, minimum SpO2, AH%SPT, ODI, and AHI.The sensitivity of ODI in detecting patients with severe OSA in relation to the STOP bang questionnaire was 100%, 96.9%, and 88.7%, respectively. Conclusion- A significant association between AHI , ESS, STOP bang and ODI renders nocturnal oximetry a cost-effective method for reliably screening patients with severe OSA.