Condition Guide

Sleep Apnea

Name: Sleep Apnea: Blood Tests, Causes & Risk Factors
Creator: Suman Konda
Published: 2026-07-05

Sleep apnea causes repeated breathing pauses during sleep, disrupting oxygen delivery. While diagnosed by sleep study, several blood tests reveal its causes and complications.

Written by Suman Konda, PharmD, Clinical Pharmacist · Based on peer-reviewed sources · Editorial policy · Not medical advice

Last updated: 01 August 2026 · How we check our content

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?

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

Chronic Insomnia. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK526136