Standard Diagnostic Test For Sleep Apnea Does Not Detect Condition In Many Patients

August 12, 2000

Testing for two nights in a sleep center rather than the standard one night avoids false-negative results and misdiagnoses connected with sleep apnea syndrome, according to a study published in the August 2000 issue of CHEST.

Writing in the peer-reviewed journal of the American College of Chest Physicians, Olivier Le Bon, M.D., from the Brugmann Hospital Sleep Unit, Brussels, Belgium, along with six associates, studied 243 patients admitted to the unit between 1992 and 1998 to determine whether they had sleep apnea-hypopnea syndrome. Apnea occurs when tissues at the back of the throat periodically collapse, causing blockage, and forcing the sleeper to gasp for air. Rarely does it cause the victim to fully awaken.

In this study, all individuals tested suffered from excessive daytime sleepiness, fatigue, snoring, or a description by a bed partner of sleep interruption.

In the United States, sleep apnea affects an estimated 18 million persons, with less than 1 million being aware of their problem. For victims, daytime sleepiness can be so profound that it affects business and social life. Sometimes sufferers fall asleep at the wheel, causing motor vehicle accidents. The costs to society from loss of productivity, industrial and personal accidents, plus medical bills, is estimated to be over $60 billion per year. Once detected, sleep apnea can be treated with continuous positive airway pressure (CPAP), as well as other therapies.

"This study proves it is worth performing two consecutive sleep test sessions or at least a second one when the results of testing on the first night are negative in patients admitted for apnea detection," commented Dr. Le Bon.

Study Methodology

The researchers defined an episode of apnea as greater than 80 percent reduction in airflow (almost total breathing cessation) for at least 10 seconds during sleep. A hypopneic episode was defined as a 50 to 80 percent reduction of airflow accompanied either by a reduction in oxygen saturation of more than 3 percent or by arousal from sleep. To determine respiratory events, the investigators made polysomnography recordings on each of two nights. A reading of more than 20 events per hour on the apnea-hypopnea index (AHI) was considered sleep apnea syndrome.

In the study, 101 patients had an AHI of more than 20 events per hour. Of these individuals, 74 tried nasal continuous positive airway pressure (CPAP) on night two.

These persons were not part of the night two comparative data to determine the value of a second test. A subgroup of 169 patients who did not use an CPAP device constituted the comparison group of night one versus night two.

During night two, 62 patients shifted up to a plus 20 AHI score, almost twice the 32 whose scores dropped on the second night. The scientists said this finding "underscores the larger proportion of subjects having more severe sleep events in night two."

Conclusions

"The comparison between night one and night two recordings," said Dr. Le Bon, "indicates a clear classic first-night effect (on night one) as shown by a shorter sleep period and less total sleep time, worse sleep efficiency, longer sleep onset latency, more wake time after sleep onset, a higher awakening index, less rapid eye movement sleep time, and longer rapid eye movement sleep latency."

Previous studies have concluded that one night of recording should suffice for diagnosis. The American Thoracic Society Consensus Conference on Cardio-Pulmonary Sleep Studies noted that "a single polysomnogram is sufficient to exclude clinically important sleep apnea." Based on that consensus, and the pressures of insurance providers to lower costs, most sleep laboratories follow the policy of recording only one night, and many capture only the first few hours of sleep, and using the balance of the night for a CPAP titration.

According to Dr. Le Bon, in considering the disability associated with sleep apnea/hypopnea syndrome, as well as its global cost to society, doctors must not miss the diagnosis.

"Our study confirms that an important number of patients presented false-negative results on night one, which turned out to be more frequent among severe cases," he said. "This underscores the need for a second test recording when the results of night one are negative."