Symptom · Poor sleep
A blood test cannot measure sleep, but it can measure most of the things that wreck it. A cortisol rhythm that is flat in the morning and high at night. A thyroid running fast (wired, waking at 3am) or slow (unrefreshed after nine hours). Ferritin low enough to cause restless legs and fragmented sleep. Oestradiol or testosterone falling and taking deep sleep with them. Blood sugar that dips overnight and wakes you at 4am. Low vitamin D and magnesium. Low-grade inflammation. Each is common, each is treatable, and each gets mislabelled as insomnia, stress or age when nobody looks at the blood.
Venous draw at 103 UK clinics or at home. Morning appointment, so cortisol is meaningful. Report within 48 hours of the lab receiving your sample.
Last reviewed 16 September 2026
The short answer
A blood test for poor sleep should cover morning cortisol with DHEA-S, a full thyroid panel, ferritin with iron studies, sex hormones (oestradiol and FSH, testosterone), HbA1c with fasting insulin, vitamin D, magnesium and hs-CRP. The pattern tells you which kind of bad sleep you have: can't fall asleep (cortisol, thyroid, oestrogen), can't stay asleep (blood sugar, cortisol, ferritin), or sleep and wake unrefreshed (thyroid, iron, vitamin D, inflammation). What a blood test cannot do is diagnose sleep apnoea or a primary insomnia; if the panel is clean, those are the next things to rule out.
Educational, not a substitute for a doctor. Loud snoring with witnessed pauses in breathing, or falling asleep while driving, needs a GP referral for a sleep study regardless of any blood result.
What to test
| Marker | The sleep problem it causes | What to look for | Panel |
|---|---|---|---|
| Morning cortisol, DHEA-S | Cortisol should peak on waking and fall through the day. Chronic stress flattens the morning and lifts the evening: tired all day, wired at 11pm, waking at 3am with a racing mind | Morning cortisol at either end of range (must be drawn 8 to 9am); low DHEA-S with a high or low cortisol | All panels |
| Thyroid (TSH, free T4, free T3, antibodies) | Overactive: can't switch off, night sweats, early waking, palpitations. Underactive: sleeping long and waking exhausted, needing naps | TSH below 0.4 or above 2.5 with symptoms; free T3 or T4 outside range; positive antibodies | All panels |
| Ferritin, iron studies | Restless legs, periodic limb movements, fragmented and unrefreshing sleep. Iron is needed to make dopamine, and low stores disrupt it at night first | Ferritin below 50 with restless legs; below 30 is deficiency; NICE guidance for restless legs targets ferritin above 75 | All panels |
| Oestradiol, FSH, progesterone (women) | Falling oestrogen in perimenopause causes night sweats and 3am waking; falling progesterone removes its sedative effect. The commonest new sleep problem in women over 40 | Rising FSH with low oestradiol; low luteal progesterone | Core hormones in Advanced; complete set in Ultimate and Signature |
| Testosterone, SHBG (men) | Low testosterone reduces deep sleep and is itself worsened by poor sleep and sleep apnoea, a loop that runs both ways | Total testosterone in the bottom quarter of range; high SHBG lowering the free fraction | Testosterone in Advanced; SHBG and free testosterone in Ultimate and Signature |
| HbA1c, fasting insulin, HOMA-IR | Insulin resistance means unstable overnight glucose; a dip at 3 to 4am triggers adrenaline and cortisol and you wake sharply, often hungry or sweating | HbA1c above 38; fasting insulin above 10 mIU/L; HOMA-IR above 2 | HbA1c in all; insulin and HOMA-IR in Ultimate and Signature |
| Vitamin D, magnesium | Both are linked to sleep quality and duration; low vitamin D with daytime fatigue, low magnesium with cramps, restless legs and difficulty settling | Vitamin D below 50 nmol/L; magnesium at the bottom of range | All panels |
| hs-CRP | Low-grade inflammation fragments sleep and blunts its restorative effect; it is also a consequence of sleep apnoea, so a raised result with snoring points to a sleep study | Above 1 mg/L worth explaining; above 3 with snoring, ask about apnoea | All panels |
Thresholds are UK laboratory conventions and NICE guidance where it exists. Your report reads each result against the others. Guides: cortisol, thyroid, ferritin, perimenopause, testosterone, insulin resistance, vitamin D, hs-CRP.
Read it in context
Can't fall asleep
Evening cortisol high, morning cortisol flat, TSH suppressed or free T3 high, or oestradiol falling. This is a stress-hormone or thyroid picture. It responds to a cortisol rhythm fixed from the morning end (light, timing, caffeine cut-off) and, where the thyroid is involved, treatment. Stress blood test.
Can't stay asleep
Fasting insulin raised, HbA1c creeping, ferritin under 50, or FSH rising with low oestradiol. The 3am wake is usually a glucose dip, a restless-leg arousal, or a hot flush. Each has a different fix, and the blood picture says which.
Sleep and wake exhausted
TSH high or free T3 low, ferritin under 30, vitamin D under 50, hs-CRP raised. Unrefreshing sleep is the classic underactive-thyroid and iron-deficiency complaint. If the panel is clean and you snore, this is the sleep apnoea pattern and needs a sleep study. Always tired, tests normal?
Which panel
Advanced
74 biomarkers · £269
Morning cortisol and DHEA-S, full thyroid with antibodies, ferritin with iron studies, vitamin D, magnesium, HbA1c, hs-CRP, core sex hormones. Everything except fasting insulin and the complete hormone set.
View AdvancedAll eight causes
Ultimate
114 biomarkers · £349
Adds fasting insulin and HOMA-IR for the 3am glucose dip, the complete hormone set including progesterone, SHBG and free testosterone, plus Lp(a), cystatin C and tumour markers.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. Adds an autoimmune and digestive profile and neurological markers, for poor sleep alongside gut or autoimmune symptoms.
View SignatureClinic draw £19. At-home £39. Book a morning slot and fast from 10pm: cortisol and insulin both depend on it. Pay monthly available.
Honest comparison
Three things. It cannot diagnose sleep apnoea, which needs an overnight study and is the commonest serious sleep disorder in men over 40 and anyone overweight. It cannot diagnose primary insomnia, the kind that is about conditioning and habit rather than chemistry, which is treated with CBT-I and responds well to it. And it cannot see your sleep environment, your screen at midnight or your fourth coffee. What it does is rule the physical causes in or out, which matters because they are treated completely differently: nobody should be doing CBT-I for a ferritin of 12 or a TSH of 8. If you have snoring with witnessed pauses, ask your GP for a sleep study first and do the bloods alongside; if you do not, do the bloods first and let the result decide the next step. What to ask your GP for.
After your result
Stress-hormone, thyroid, iron, hormonal, metabolic or inflammatory, and which of the three kinds of bad sleep it produces, so the fix matches the cause.
Iron, vitamin D and magnesium are corrected with supplements at the right dose; blood sugar and cortisol rhythm respond to timing of food, light and exercise. A thyroid or hormone result needs a prescriber, and the report tells you which results to show them.
Ferritin takes about twelve weeks to refill and restless legs settle as it does. The second report shows the numbers moving with the sleep. Retest plans.
FAQs
It can show the physical causes: a disrupted cortisol rhythm, an over- or underactive thyroid, low ferritin, falling oestradiol or testosterone, insulin resistance, low vitamin D or magnesium, and inflammation. Together those explain most poor sleep with a physical cause. It cannot diagnose sleep apnoea or primary insomnia.
Fasting insulin and HbA1c (an overnight glucose dip), morning cortisol (a disrupted rhythm), ferritin (restless legs), and in women oestradiol and FSH (hot flushes). The Ultimate panel covers all of them in one draw.
Yes. Iron is needed to make dopamine, and low ferritin is the commonest treatable cause of restless legs and fragmented sleep. NICE guidance for restless legs recommends iron when ferritin is below 75, well above the lab's deficiency cut-off, which is why a "normal" ferritin of 35 can still be the problem.
No. Sleep apnoea is diagnosed with an overnight sleep study. A blood test can raise suspicion (a raised hs-CRP, a high red cell count, low testosterone in a man who snores) and can rule out the other causes, but if you snore loudly with pauses in breathing, ask your GP for a sleep study.
Very often. Falling oestradiol causes night sweats and 3am waking, and falling progesterone removes its sedative effect. It usually arrives with heavier periods and lower ferritin, which compound it. Oestradiol, FSH and progesterone are in the Ultimate panel. Perimenopause blood test.
Yes, and it must be in the morning. Cortisol only means something between about 8 and 9am, and fasting insulin needs an overnight fast. Nothing but water from 10pm the night before. Full preparation guide.
Advanced and Ultimate reports are delivered within 48 hours of the laboratory receiving your sample. Signature takes around 12 working days.
All eight causes in one morning venous draw, at 103 UK clinics or at home, with a report within 48 hours that says which kind of bad sleep you have and what to do about it.
Brain fog · Always tired · Stress · Menopause · Find a clinic
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