Still exhausted after eight hours?

1. Can a blood test find sleep apnoea?

No, and any test that says otherwise is overselling. Apnoea is a breathing event. It is counted while you sleep, not measured in a sample. The NHS route is short and it is free.

“If a GP thinks you might have sleep apnoea, they may refer you to a specialist sleep clinic for tests.”

— NHS, Sleep apnoea

Those tests usually happen at home. You wear a small monitor overnight, and it records your breathing and your heart. The result is an AHI score, which counts breathing interruptions per hour. The NHS reads 5 to 14 as mild, 15 to 30 as moderate, and above 30 as severe.

The signs that should send you down that route are mostly the ones you cannot see yourself. The NHS lists breathing that stops and starts, gasping or choking noises, loud snoring, and waking often. In the daytime it looks like heavy tiredness, poor concentration, mood changes and morning headaches.

Ask whoever sleeps near you. A partner noticing pauses in your breathing is worth more here than any number in this guide.

2. What else leaves you exhausted after a full night?

This is where blood earns its place. Several ordinary things produce the same flat, unrefreshed morning, and every one of them is measurable.

• An underactive thyroid. Slows everything down, including how rested you feel
• Low iron stores. Ferritin can be low long before anaemia shows up
• Low vitamin B12 or vitamin D. Both common in the UK, both easy to read
• Quiet inflammation. CRP rising in the background of something else

The thyroid one is worth pausing on. It does not simply imitate apnoea. It appears to keep company with it.

In August 2026, researchers at the Federal University of São Paulo reported an analysis of 761 adults from the EPISONO sleep database. Hypothyroidism was found in 12.6% of them, and 49.5% of that group also had obstructive sleep apnoea.

Read that carefully. It is a snapshot of one population, so it shows company, not cause. It still makes the practical point. If your thyroid has never been read, a thyroid result is a cheap thing to know before you go anywhere near a sleep clinic waiting list. Our thyroid blood test guide covers what TSH and the T4 reading actually mean.

For the wider tiredness picture, our always tired guide walks through the full set, and the full blood count guide explains the standard panel most people are given first.

3. Which blood markers travel with sleep apnoea?

Broken breathing overnight leaves a trail in daytime chemistry. These markers do not identify apnoea. They describe the load it puts on the rest of you, and they are worth knowing either way.

HbA1c, your three-month blood sugar average. A 2021 study in the Journal of Endocrinological Investigation looked at 90 obese adults without diabetes. Three quarters had sleep apnoea. Their HbA1c averaged 5.8% against 5.4% in those without it. The NHS also lists type 2 diabetes among the problems untreated sleep apnoea can lead to.

hs-CRP, a sensitive inflammation marker. In the Korean Genome and Epidemiology Study, published in PLOS One in 2016, people with moderate to severe apnoea were 1.7 to 2.0 times more likely to sit in the highest hs-CRP band. That held after adjusting for body fat and waist measurements.

Testosterone, in men. A 2021 study in Frontiers in Endocrinology followed 104 severely obese men. Average total testosterone fell from 16.6 to 11.3 nmol/L as apnoea severity climbed. The relationship runs both ways, and poor sleep on its own moves the number, as our sleep and testosterone guide explains.

Where these sit in our range, if you want them read at home. The General Energy & Wellness panel (£149) covers TSH, free T4, CRP, cortisol, vitamin D, vitamin B12 and magnesium. Note that its CRP is the standard version, not the high-sensitivity one.

The Thyroid & Vital Organs panel (£159) adds free T3 to the thyroid picture alongside kidney and liver markers. HbA1c and hs-CRP sit together in the Advanced Heart Health panel (£159), and testosterone in the Complete Male Hormones panel (£119). None of these panels reads all of them, so pick the question you most want answered.

4. What should you do first?

Order matters here, and it is not the order a health website usually gives you.

• If someone has seen you stop breathing, see your GP. A blood test is not a substitute for that referral
• If you fall asleep at the wheel, treat it as urgent. Speak to your GP now, not next month
• If nobody reports pauses, start with bloods. Thyroid, iron and the vitamins explain a lot of flat mornings
• If you already know you have apnoea, read the markers. HbA1c and inflammation are the ones that carry forward

There is also a legal point people miss. DVLA rules say you must tell them if you have confirmed moderate or severe apnoea with excessive sleepiness. You must not drive until the sleepiness has gone, or your symptoms are controlled and you are following treatment.

A home blood test measures markers. It does not diagnose anything, and it cannot see a night of interrupted breathing. What it can do is take the guessable causes off the table, so the conversation with your GP starts further along.

5. Frequently asked questions