The Epworth Sleepiness Scale (ESS) has been shown to have only moderate reproducibility in repeat assessments of patients in a sleep clinic population.

It should probably not be used in clinical settings to monitor the impact of therapeutic interventions in individuals or for prioritising access to services such as sleep studies, according to the findings of a Sydney study.

The study, comprising 108 adult patients, compared the ESS in patients at a first specialist visit and again on the night of diagnostic polysomnography. The test-retest interval was a median of 64 days.

Most patients (90%) had sleep-disordered breathing (Respiratory Disturbance Index >5 events/hr) and 26% had severe disease ( ≥30 events/hour).

The study found the range of scores across the two measurements was 0-23. The mean score was 10.1 at the clinic visit and 9.0 at polysomnography.

“Although the mean difference (bias) was 1.1, the 95% limits of agreement were between −8.5 and +10.6. An absolute difference in scores of at least 3 was observed in 60 (56%) participants,” the study said.

There was no correlation between ESS and RDI and no evidence that factors such as age, gender, BMI, medication use or sleep study parameters were significant predictors of test–retest variability in the ESS score.

“Together these results raise concerns about the utility of the ESS as a reliable measure of EDS in a sleep clinic population,” the study said.

Senior investigator Dr Hima Vedam, from the respiratory and sleep medicine department at Liverpool Hospital, told the limbic their findings were also consistent with other studies.

“The Epworth came about at a time when sleep medicine was very, very new but we are always developing and we are always learning new things. It’s become apparent we need to re-assess what we have been using,” she said.

While it was initially found to have some utility in differentiating between different groups of patients, the ESS certainly shouldn’t be used to monitor individual patients.

“It was never originally designed to be a repeatable tool and the whole purpose of this paper is to show if you keep doing it, in a proportion of patients you are going to get a different answer.”

It was not ideal for people from non-English speaking backgrounds and older people, Dr Vedam said.

“In terms of the number of questions, it can become harder and harder to answer all of the questions. A lot of older people especially find the Epworth questions sometimes hard to answer.”

She said part of the reason the Epworth was still used was because there was little else.

There was a three-item Observation and Interview Based Diurnal Sleepiness Inventory (ODSI) but more importantly, the potential to create more objective tools using technology and measures such as eye closures.

“What it does highlight especially in this day and age, is we do need to look to better objective measurement of excessive daytime sleepiness and a lot of people are working on this.”