Sleep study: how sleep apnea is actually diagnosed

A sleep study is the investigation that establishes sleep apnea. It records a full night of your breathing, oxygen level, heart rate and body position, and produces one number: the average count of breathing stops per hour of sleep. No questionnaire, no blood test and no app can replace that number.

That is the core of it, and it is exactly why this article exists.

Because most men who suspect something is wrong with their sleep have no idea what to ask, who to ask, or what happens next. Below is the whole route, from the conversation at your doctor to the result on paper.

How do you test for sleep apnea?

There are two routes. With a home recording, also called polygraphy, you take equipment home, fit it yourself and sleep in your own bed. With polysomnography you sleep a night in a sleep centre, with more sensors and staff monitoring.

Which of the two you get depends on your complaints and on what the doctor wants to rule out. The table below sets them side by side.

In practice the home recording is the most common first step when obstructive sleep apnea is clearly suspected. Its big advantage is that you sleep the way you normally sleep.

Polysomnography is more extensive and needed when the question is more complicated, for instance with suspected central apnea, restless legs or narcolepsy.

How do you get a sleep study?

Through your doctor. They assess your complaints, look at your blood pressure, weight and neck circumference, and on reasonable suspicion refer you to a lung specialist, ENT surgeon or neurologist, depending on the hospital and your pattern of complaints.

That conversation goes more easily if you arrive with concrete information. Bring how long you have been tired, whether anyone has seen breathing stops, how often you get up at night to urinate, whether you wake with headache, and where your blood pressure sits.

Chung and colleagues developed STOP-BANG in 2008, a short validated questionnaire that estimates the likelihood of obstructive sleep apnea. Eight yes-no questions on snoring, tiredness, observed stops, blood pressure, BMI, age, neck circumference and sex. Three or more yes answers count as raised likelihood.

That list establishes nothing. It only helps your doctor judge whether an investigation is worthwhile. The full list is in the pillar on sleep apnea in men.

For a plain-language Dutch explanation of what a GP does with sleep complaints, Thuisarts is the best starting point.

What gets measured during a sleep study?

The core is your breathing. A band around your chest and belly records your breathing movements, a small tube at your nose measures airflow, and a clip on your finger measures oxygen saturation and heart rate.

Body position is recorded almost always as well. That sounds like a detail and is not: in a subset of people the breathing stops occur mainly while lying on their back, and that changes the treatment.

With polysomnography, electrodes are added that measure brain activity, eye movements and muscle tone. That shows which sleep stage you were in at the moment your breathing faltered.

Uncomfortable? Somewhat, but less than people expect. Most people sleep reasonably normally during a home recording.

What does the result of a sleep study mean?

The main outcome is the apnea-hypopnea index, the AHI. That is the average number of breathing stops and severe reductions per hour of sleep. The classification below is used internationally.

Alongside the AHI, the doctor looks at how far your oxygen drops and how long it stays low. Take two men who both come back with an AHI of 18: if one dips to 92 percent during his breathing stops and the other to 78, they look identical on paper and are dealing with something quite different in reality.

Your complaints count towards the decision too. An AHI of 12 in someone fading out behind the wheel weighs more than the same 12 in someone without daytime complaints.

Can you test for sleep apnea at home with a smartwatch?

Not reliably. Some watches and rings measure oxygen saturation and flag dips, and one or two manufacturers now offer an approved apnea feature. What they do not do is measure airflow at your nose, and that is precisely what the diagnosis rests on.

What they are good at: making visible a pattern that gives you reason to see a doctor. A chart with recurring oxygen dips is a perfectly good conversation opener.

Snoring apps are a step weaker again. They record sound, not breathing, and the silences between the snores are the interesting part.

My own line on this: use them to convince yourself to get something looked at, not to reassure yourself.

What can blood testing do here?

Blood does not establish sleep apnea. What blood does is bring the other explanations for your fatigue into view before you enter a referral pathway: your thyroid, your iron and ferritin, your blood sugar and your testosterone.

That is worth more than it sounds. Sleep complaints often have more than one cause at once, and an underactive thyroid can both mimic the complaints and worsen the apnea itself.

Then there is haematocrit. It can run higher with sustained night-time oxygen dips, and it is a value that runs alongside anyway in men using testosterone.

You can arrange this yourself with the male hormone panel, without a referral. How that works is in blood test without a referral. The values themselves are on haematocrit and TSH.

What it comes down to

A sleep study is less invasive than most men imagine. In most cases it is a small box you take home, a night in your own bed, and a result with a number on it.

What makes the investigation valuable is that it is the only thing that genuinely answers the question. Every other signal, from snoring to a STOP-BANG score, is a clue.

If you are unsure, write your complaints down, let blood rule out the other explanations first, and take that to your doctor. The symptoms are in sleep apnea daytime symptoms, the treatments in sleep apnea device.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Chung F, et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology, 2008. PMID 18431116
• Heinzer R, et al. Prevalence of sleep-disordered breathing in the general population: the HypnoLaus study. The Lancet Respiratory Medicine, 2015. PMID 25682233
• Benjafield AV, et al. Estimation of the global prevalence and burden of obstructive sleep apnoea. The Lancet Respiratory Medicine, 2019. PMID 31300334