Blood tests related to sleep apnea
| Test | Why it's relevant | What to look for |
|---|---|---|
| TSH (Thyroid) | Hypothyroidism is a reversible cause of sleep apnea | Elevated TSH = underactive thyroid |
| Fasting Blood Sugar / HbA1c | Diabetes and sleep apnea are strongly linked | Glucose >126 mg/dL or HbA1c >6.5% |
| CBC (Red blood cells) | Chronic low oxygen raises red cell count (polycythaemia) | Raised haematocrit / haemoglobin |
| Lipid Profile | Sleep apnea raises cardiovascular risk | Raised LDL, raised triglycerides |
| Testosterone (men) | Low testosterone is associated with sleep apnea | Low testosterone in obese men |
| CRP | Sleep apnea causes chronic systemic inflammation | Mildly elevated CRP |
What is sleep apnea?
Types of sleep apnea
Obstructive Sleep Apnea (OSA) is the most common type — the throat muscles relax during sleep and the airway collapses, blocking breathing repeatedly throughout the night. Each pause (apnoea) typically lasts 10–30 seconds and may occur hundreds of times per night. Central sleep apnea (CSA) is less common — the brain fails to send proper signals to breathing muscles. Complex/mixed sleep apnea combines both types. Sleep apnea is significantly under-diagnosed — it is estimated that 80% of people with moderate-to-severe OSA are undiagnosed.
Risk factors and causes
| Risk Factor | How it contributes |
|---|---|
| Obesity (BMI >30) | Fat deposits around the neck narrow the airway |
| Male sex | Men are 2–3x more likely to have OSA |
| Age over 40 | Muscle tone decreases with age |
| Large neck circumference | >17 inches (men) or >15 inches (women) increases risk |
| Hypothyroidism | Reduces respiratory drive and causes soft tissue swelling |
| Alcohol and sedatives | Relax throat muscles further |
| Structural: large tonsils, small jaw | Narrows upper airway |
Health consequences of untreated sleep apnea
Why treatment matters
Untreated sleep apnea causes chronic oxygen desaturation during sleep, which stresses every organ. Long-term consequences include: hypertension (in up to 70% of OSA patients), increased risk of heart attack, stroke and atrial fibrillation, type 2 diabetes (sleep disruption worsens insulin resistance), depression and cognitive impairment, excessive daytime sleepiness and increased accident risk. CPAP therapy (continuous positive airway pressure) — wearing a mask during sleep — is the most effective treatment and can reverse many of these complications.
Diagnosis: the sleep study (polysomnography)
Blood tests cannot diagnose sleep apnea. The definitive test is a polysomnogram (sleep study) — performed overnight in a sleep clinic or via a home sleep apnea test (HSAT). It records breathing effort, airflow, oxygen saturation, brain waves, heart rate and limb movements. The Apnea-Hypopnea Index (AHI) measures severity: mild (5–14 events/hour), moderate (15–29 events/hour) or severe (≥30 events/hour).
Questions to ask your doctor
- Should I have a home sleep test or an in-lab sleep study?
- Could my thyroid be contributing to my sleep apnea?
- What is my AHI score and what severity does that indicate?
- Is CPAP the right treatment for me, or are there alternatives?
- How does sleep apnea affect my heart and diabetes risk?