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Sleep Apnea

Sleep apnea causes repeated breathing pauses during sleep, disrupting oxygen delivery. While diagnosed by sleep study, several blood tests reveal its causes and complications.1

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

Last reviewed and updated: · How we check our content

What sleep apnea is

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Sleep apnea causes repeated breathing pauses during sleep, disrupting oxygen delivery. Obstructive sleep apnea (OSA) is the most common type: the throat muscles relax during sleep and the airway collapses, blocking breathing repeatedly through the night. Each pause 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 the breathing muscles — and complex or mixed sleep apnea combines both. Sleep apnea is significantly under-diagnosed: an estimated 80% of people with moderate-to-severe OSA do not know they have it.1

How sleep apnea is usually evaluated

Diagnosis is by sleep study, not blood tests — but screening and workup bloods each have their place:

StepWhat it does
STOP-BANG screening8-item questionnaire: snoring, tiredness, observed apnoeas, blood pressure, BMI, age, neck circumference, gender — 5–8 points is high risk
PolysomnogramThe definitive test: overnight recording of breathing effort, airflow, oxygen saturation, brain waves, heart rate and limb movements
Home sleep apnea testSimplified alternative for straightforward suspected OSA
AHI severityApnea-Hypopnea Index: mild 5–14, moderate 15–29, severe ≥30 events per hour
Workup blood testsTSH (hypothyroidism is a reversible cause), HbA1c/glucose, full blood count (polycythaemia), lipid profile, testosterone in men, CRP

The blood tests are for the consequences and the company OSA keeps — diabetes, thyroid disease, cardiovascular risk — not for the diagnosis itself. Untreated hypothyroidism can both cause and dramatically worsen OSA, which is why TSH is checked.3

Your next steps after a sleep apnea diagnosis

  1. Discuss home test versus in-lab study. Ask which is appropriate for your situation — and what your AHI score and severity band mean in practical terms.
  2. Understand the first-line treatment. CPAP (continuous positive airway pressure), worn during sleep, is the most effective treatment and can reverse many complications. For those who cannot tolerate it, a custom oral appliance repositioning the jaw is a recognised alternative for mild-to-moderate cases.2
  3. Take the cardiovascular link seriously. Up to 70% of people with OSA have hypertension; loud snoring plus daytime sleepiness plus witnessed pauses is the combination that should trigger a sleep study, not another year of poor sleep.
  4. Check the reversible contributors. Ask whether your thyroid has been checked, and review alcohol and sedative use, which relax throat muscles further.
  5. Address the weight connection. Obesity is the strongest modifiable risk factor — fat deposits around the neck narrow the airway — so weight management is part of the long-term plan.

Practical notes

Sleep apnea is diagnosed from what happens at night, so a two-week sleep diary before your appointment is genuinely useful: bedtime and wake time, loudness of snoring, any witnessed pauses or gasping (ask your partner), morning headaches, and a note on daytime sleepiness — including any drowsy driving, which you should mention honestly. If you start CPAP, most machines record nightly usage hours, which your doctor will review.

Details that help the sleep physician include witness accounts of your breathing at night, your weight history, alcohol and sedative use (especially near bedtime), nasal congestion or allergies, all current medicines, and any history of hypertension, atrial fibrillation or diabetes — conditions that travel with sleep apnea and influence how urgently it is investigated.

The lifestyle measures most often discussed are gradual weight management, avoiding alcohol and sedatives in the evening, sleeping on your side rather than your back, treating nasal congestion, and keeping a regular sleep schedule. Smoking cessation is usually mentioned too. These steps can reduce severity, particularly in mild cases, alongside whatever treatment your doctor recommends.

Follow-up depends on the path taken: after starting CPAP, an early review checks mask fit, usage hours and symptom improvement, with periodic reviews thereafter. A repeat sleep study is typically advised after major weight change, if symptoms persist despite treatment, or at intervals your sleep physician sets.

In India

An overnight polysomnography at a sleep lab typically costs ₹8,000–₹20,000, while a home sleep apnea test — suitable for straightforward suspected cases — usually costs a few thousand rupees; prices vary widely by city and facility.

For any blood tests ordered alongside the sleep evaluation (thyroid function is commonly checked), look for NABL-accredited laboratories, which follow standardised quality processes, with home sample collection available in major cities. The sleep study itself is done at a lab or with a home-test device provided by the sleep centre. Whatever a lab's website says about normal values, the reference range printed on your own report is the one that counts, since ranges differ between machines and assay methods.

Frequently asked questions

What is the difference between obstructive and central sleep apnea?

Obstructive sleep apnoea (OSA) — by far the more common form — is caused by collapse of pharyngeal soft tissue during sleep: airflow ceases despite continued breathing effort. Central sleep apnoea (CSA) is caused by failure of the respiratory drive: the brain fails to send the signal to breathe. Treatment differs fundamentally between the two.

How is sleep apnea diagnosed?

Blood tests cannot diagnose it. The definitive test is a polysomnogram (sleep study), performed overnight in a sleep clinic or via a home sleep apnea test — recording breathing effort, airflow, oxygen saturation, brain waves, heart rate and limb movements. The Apnea-Hypopnea Index (AHI) measures severity: mild 5–14, moderate 15–29, severe 30 or more events per hour.3

What is the STOP-BANG questionnaire?

A screening tool identifying patients at high risk for OSA who need sleep studies. One point each for: loud Snoring, daytime Tiredness, Observed apnoeas, blood Pressure, BMI above 35, Age above 50, Neck circumference above 40 cm (men) / 38 cm (women), and male Gender. A score of 5–8 is high risk; 3–4 intermediate; 0–2 low.

Can blood tests diagnose sleep apnea?

No — but they identify the metabolic consequences and comorbidities that modify treatment priority. TSH matters because hypothyroidism is a reversible cause of sleep apnea; HbA1c and fasting glucose because OSA and type 2 diabetes are strongly linked; and a full blood count because chronic low oxygen raises red cell count (secondary polycythaemia).

What happens if sleep apnea is left untreated?

Chronic oxygen desaturation stresses every organ: hypertension (in up to 70% of OSA patients), increased risk of heart attack, stroke and atrial fibrillation, worsened insulin resistance and type 2 diabetes, depression and cognitive impairment, and excessive daytime sleepiness with increased accident risk. CPAP therapy is the most effective treatment and can reverse many of these complications; a custom oral appliance is a recognised alternative for mild-to-moderate cases who cannot tolerate CPAP.12

My partner says I snore loudly — does that mean I have sleep apnea?
Not necessarily — snoring is common and most loud snorers do not have sleep apnea. What points more towards apnea is witnessed pauses in breathing, gasping or choking at night, morning headaches, and significant daytime sleepiness. Only a sleep study can confirm it, so loud snoring plus any of those features is worth discussing with your doctor.
Can I do the sleep study at home instead of spending a night in a lab?
Often, yes — home sleep apnea tests are widely used for straightforward suspected obstructive sleep apnea and are more comfortable and cheaper. But they record fewer signals, so an in-lab polysomnography is still preferred if central apnea, other sleep disorders, or serious heart or lung disease is suspected. Your sleep physician decides which suits your case.
Will losing weight cure my sleep apnea?
Weight loss can substantially improve sleep apnea and occasionally resolve mild cases, since excess weight around the neck narrows the airway — but it is not guaranteed, and thin people get sleep apnea too. Treat it as one part of management to discuss with your doctor, not a reason to delay testing or treatment.
Is it safe to keep driving if I might have untreated sleep apnea?
Excessive daytime sleepiness measurably raises accident risk, and falling asleep at the wheel is one of the most serious consequences of untreated apnea. If you feel drowsy while driving, avoid it and say so plainly to your doctor — effective treatment usually improves alertness, which is another reason not to postpone evaluation.

References

Sources cited on this page. PubMed links open the original abstract.

  1. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med. 1993;328(17):1230–1235. PMID 8464434 · doi:10.1056/NEJM199304293281704
  2. Ramar K, Dort LC, Katz SG, et al. Clinical Practice Guideline for the Treatment of Obstructive Sleep Apnea and Snoring with Oral Appliance Therapy. J Clin Sleep Med. 2015;11(7):773–827. PMID 26094920 · doi:10.5664/jcsm.4858
  3. Kapur VK, Auckley DH, Chowdhuri S, et al. Clinical Practice Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea. J Clin Sleep Med. 2017;13(3):479–504. PMID 28162150 · doi:10.5664/jcsm.6506
Medical Disclaimer: This page is for general educational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis, treatment, and personalised advice.
Written and medically reviewed by Suman Konda, Clinical Pharmacist · Sources linked to PubMed · Not medical advice: see our disclaimer