How is Obesity Hypoventilation Syndrome (OHS) diagnosed and what tests are required?

Reviewed by Yoshinori Abe, MD

Internal Medicine

Obesity Hypoventilation Syndrome (OHS) is diagnosed when a person with obesity shows low blood oxygen and elevated carbon dioxide levels during wakefulness, without another cause of hypoventilation. Doctors typically confirm OHS using arterial blood gas analysis, pulmonary function tests, and overnight sleep studies (polysomnography) to detect associated sleep apnea.

If you're experiencing daytime fatigue, shortness of breath, or disrupted sleep, understanding your symptoms early is critical. OHS can lead to serious complications like heart failure and pulmonary hypertension if left untreated, so identifying warning signs promptly gives you the best chance at effective management. Take a free, instant, online symptom check to better understand what may be causing your symptoms and confidently navigate your next steps with your healthcare provider.

Reviewed for medical accuracy: 07/15/2026

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Explanation

To diagnose Obesity Hypoventilation Syndrome (OHS), doctors look for signs of low oxygen and high carbon dioxide in the blood. This is often done using a blood gas analysis, which measures the levels of oxygen and carbon dioxide.

Additionally, a sleep study might be required to see how breathing changes during sleep. This helps in understanding if the person stops breathing or has shallow breathing when asleep.

Key steps in diagnosing OHS include:

Blood Gas Analysis: Checks for high carbon dioxide and low oxygen levels.
Sleep Study (Polysomnography): Observes breathing patterns during sleep.
Body Mass Index (BMI): Used to confirm obesity.

These tests help doctors understand if someone has OHS and how it affects their breathing, especially during sleep. If you're experiencing symptoms like daytime fatigue, shortness of breath, or poor sleep quality, take our free AI symptom checker to learn more about what might be causing your symptoms.

(References)

Neborak JM, & Mokhlesi B. (2025). Evaluation and Management of Obesity Hypoventilation .... Sleep medicine clinics, 41136085.
Mokhlesi B, Masa JF, Brozek JL, Gurubhagavatula I, Murphy PB, Piper AJ, et al. (2019). Evaluation and Management of Obesity Hypoventilation .... American journal of respiratory and critical care medicine, 31368798.
Kaw R, Wong J, & Mokhlesi B. (2021). Obesity and Obesity Hypoventilation, Sleep .... Anesthesia and analgesia, 33857968.

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