Don’t get your hopes up if your first sleep study is negative for sleep apnea.

Better have a second sleep study done because the first one may have missed it.

Meyer et al’s report in the journal Chest states “that a single negative sleep study is insufficient to exclude OSA in patients with one or more clinical markers for the disease.”

Eleven patients had clinical features indicative of sleep apnea. The first sleep study for all 11 patients was negative. The second study was positive for six of the patients.

Six out of 11 patients’ first sleep study missed their obstructive sleep apnea. That’s not encouraging.

The study authors point out that it’s not clear why the sleep apnea was missed in those six patients. And the patients even had a high clinical suspicion for OSA.

Theory Why First-Time Sleep Study Might Miss Sleep Apnea

The authors speculate that pharyngeal resistance was not high enough on the baseline study for the patients to yield apnea or hypopnea events.

However, the resistance was high enough on the second night. Nevertheless, don’t take this to mean that pharyngeal resistance was normal on that first night.

Another speculation is that on the second night, the patients with positive results had more nasal blockage than they had on the first night.

Nasal congestion could affect absence or presence of apneas and hypopneas.

Next up is the idea that on the second night, the patients spent more time on their back, which encourages airway collapse due to gravity.

But the authors note that their study did not track body positions during the polysomnography.

Maybe the six patients had ingested alcohol prior to the study. Liquor relaxes the pharyngeal architecture, making it easier for the airway to collapse.

However, the patients had been instructed to avoid alcohol, and the study authors don’t believe that noncompliance with this instruction was a factor.

The authors also ruled out what they call a “first night effect,” in that the first time a person sleeps in a lab, they’re uptight and thus, their normal sleeping pattern is absent.

But the authors note that no difference in sleep parameters was evident.

So we now know that a first time sleep study is not to be taken as the gospel, as it can miss sleep apnea.

This then begs the question: How many negative sleep studies are required to confidently rule out obstructive sleep apnea?

The paper cites a study by Dean and Chaudhary in which three people were diagnosed with obstructive sleep apnea upon a third study – after two false negative ones. The criterion was that of over five events per hour.

Because of this, Meyer et al believes that it’s possible that a third study could have been positive for OSA in some of the patients who were negative for both nights.

The paper concludes that polysomnography can miss obstructive sleep apnea, even though it’s the gold standard for diagnosis.

Night to night variability exists with sleep disordered breathing, “raising the possibility of missing the diagnosis of this serious disease,” says the report.

“Our prospective study shows that a significant number of patients with OSA can be missed with one study alone.”

This is unnerving, especially since the study subjects all had presented with significant predictive clinical risk factors for OSA.

False Negative Sleep Study Not Related To…

• Sleep architecture
• Pattern of risk factors
• Interval between test nights
• Small amount of rapid eye movement (REM; dreaming stage) on the first night

What Missed Sleep Apnea by a Study
Might Be Influenced By…

• Absence or presence of nasal congestion
• Abnormal upper airway anatomy
• Disruptive environmental factors (e.g., increasing fatigue from workplace stress as the test date nears)

Source: can study miss sleep apnea