WASHINGTON (FRONTLINE MEDICAL NEWS) – Oxygen desaturation index (ODI) scores showed significant variation across two software systems, a study showed.

In 106 patients, a comparison of ODI scores assessed using the ResMed ApneaLink Plus system (AL) and the Compumedics Grael Profusion PSG3 system (Comp) showed a bias of 4.4 events per hour (95% limits of agreement, –5.8 to 14.6 events per hour) for 4% desaturations and a bias of 7.1 events per hour (95% limits of agreement, –6.4 to 20.6 events per hour) for 3% desaturations (J Clin Sleep Med. 2017;13[4]:599-605).

This may be problematic for physicians evaluating patients during sleep studies who rely on ODI scores at 3% and 4% desaturations to create accurate apnea severity assessments, the investigators said.

“[The] wide limits of agreement in our study highlights that clinicians cannot be confident that an ODI4% recorded in the AL is the same as that recorded in the Comp. The variability was even greater for ODI3%,” wrote Yvonne Ng, MBBS, of the department of lung and sleep medicine, Monash Health, Victoria, Australia, and her colleagues. “The differences are large enough to significantly affect diagnostic thresholds for OSA [obstructive sleep apnea] and, in particular, moderate-severe OSA.”

Researchers gathered data from patients undergoing sleep analysis at the Monash Medical Centre, who were, on average, 47 years of age, had a body mass index score of 32 kg/m2, and had an apnea hypopnea index (AHI) of 23.2.

ODI3% scores analyzed through Comp diagnosed 66 patients with OSA (ODI3% greater than or equal to 5 events per hour), while desaturation events analyzed through the AL system diagnosed 90 patients, a 36% increase over Comp (P = .0002).

When researchers tested for moderate to severe OSA (ODI3% greater than or equal to 15 events per hour), 32 patients were diagnosed using the Comp system, compared with 59 patients using the AL system.

Disparities in these measurements create uncertainty among clinicians, who rely on ODI measurements for scores that are accurate and can be easily replicated using an algorithm (the previous measurement model required manual calculations), the researchers said.

“The current work demonstrates that significantly more patients would receive a diagnosis of OSA, or more particularly, moderate-severe OSA, with the AL ODI, compared to the Comp ODI,” Dr. Ng and her colleagues wrote.

“In our study, based on the calculated odds ratio, a patient has 2.9 times greater odds of a diagnosis of moderate-severe OSA if an AL oximeter is used, compared to a Comp oximeter.”

When sensitivity scores for Comp and AL were compared, AL ODI3% scores were significantly more sensitive than Comp, with sensitivity scores of 96% vs. 58%.

Using different fingers for measuring desaturation during the test or differences in algorithms used to assess ODI scores were possible sources of the disparities, the researchers noted. Differences in internal processing between the two systems were the most likely causes of the discrepancies between the data collected using each system.

“Although it is possible for the differences in ODI to be due to the use of separate fingers and arms, we think this is unlikely given the consistent bias seen when AL ODI was compared with Comp ODI in Bland-Altman analysis. … Moreover, oximeter processing factors are the likely explanation for our results as the processing parameters between the AL and the Comp are known to be different,” Dr. Ng and her investigators wrote.

They urged caution in the use of ODI measurements as a diagnostic tool for OSA or as an indicator for cardiovascular risk associated with OSA.

Because there is no universal standard for ODI measurements, the researchers were unable to determine which system was more accurate.

Several of the researchers reported receiving financial support, research equipment, or consultancy fees from various entities.

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