###### Abstract  
Diagnosis and effective treatment of obstructive sleep apnea syndrome (OSA) in adults is an important health priority. Home respiratory polygraphy is a cost-effective alternative to polysomnography in OSA. The aim of this study was to investigate the variability of two consecutive home respiratory polygraphic examinations by comparing the severity characteristics and pattern (supine dominant, continuous, etc.) variability. We examined 100 patients with clinically suspected OSA on two consecutive nights by home respiratory polygraphy. The correlation of time in bed (TIB), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and T90 of the two examinations were compared by the Pearson test. The severity ranks and nocturnal apnea patterns of the two periods were compared using Spearman and Wilcoxon tests. [PERSON]'s correlations represented a strong correlation of the AHI, ODI, and T90, but only moderate for TIB. The severity-specific correlation was the highest for AHI in the severe group. Out of 100 pairs of polygraphic examinations, 25 cases showed change in the severity ranking (decreased in 11, increased in 14); 15 cases showed a change in the polygraphic pattern (supine, non-supine, etc. ), with severity change in 6 cases. Therapy change based on the second examination was initiated in 6 cases. Our results revealed a good intra-individual correlation between the severity grades of the two nights, with the highest value in the severe cases. In some cases, the nightly variation in the polygraphic pattern may explain the change in the severity. From a therapeutic point of view, the low number of severity changes between moderate and severe groups revealed good reliability. ab 2023 13 667. 12.25.12.  
non-supine (such as REM-dependent, [10]), continuous (position- and phase-independent apneas), continuous with phasic (REM) worsening, and sporadic. The pattern and the time spent in different positions during sleep can vary from night to night and can substantially influence the severity of the breathing abnormality. Data on changes in sleep position and pattern at night are limited due to--in most cases--the conventional diagnostic process based on a single diagnostic night. The first-night effect of the examination can further reduce the reliability of the one-night sleep study [11]. These processes suggest that a single overnight test may not always be able to accurately describe the severity of the disease. The gold standard for the diagnosis of sleep apnea syndrome is the overnight polysomnographic examination [12], but availability is limited and the personnel (sleep technician) requirements are high [13]. In certain circumstances, as defined by the AASM guidelines [12,14], the polygraphic examination performed in the patient's home can be a useful tool for the diagnosis of sleep apnea syndrome. According to the AASM guideline, home sleep polygraphy is recommended if the pretest probability is high for obstructive sleep apnea syndrome [13]. There are several advantages (widespread availability, lower cost, etc.) and disadvantages (technical problems, determination of the exact sleep time, etc.) of the polygraphic examinations [15]. Due to the simplicity of this method, the repeated examination can increase the reliability of the diagnosis. Although several studies have investigated the reliability of repeated polysomnography, the current literature is limited to the night-to-night variability of the severity of OSA in home sleep polygraphy [5]. Taking together these data, the question arises about the sufficient number of sleep examinations to determine the exact severity of the sleep-related breathing abnormalities.