An overnight sleep test measures different body and brain functions when you are sleeping.

To make a diagnosis of obstructive sleep apnea, the doctor must evaluate how much oxygen is in your blood over the course of the night. If the amount of oxygen in the blood falls beneath certain levels, the doctor will know how severe the problem is and if you have airway resistance or sleep apnea.

Both lab-based and home-based sleep tests monitor more than just blood oxygen levels. Although this extra information is nice to have, it is not absolutely necessary to make a diagnosis and treatment decision.