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Patients suspected of having sleep apnea often undergo a sleep study, which may be conducted overnight at a hospital, an accredited sleep center or in the home using special equipment that monitors sleep. Prior to the sleep study, a medical history and a family history will be taken by the physician. During the history, the patient should tell the physician of any medication being taken. In addition, the patient should keep a record of periods of daytime fatigue, morning headaches and other symptoms associated with sleep apnea before and after the sleep study.

The physician may also check for the physical characteristics associated with obstructive sleep apnea, such as a large neck, enlarged tonsils and/or enlarged tongue. An electrocardiogram (EKG) may also be used to detect abnormal heart rhythms (arrhythmias) that have been associated with sleep apnea.

In an in-office sleep study, about two hours before going to sleep, the patient will be hooked up to several monitoring devices to record various measures of sleep, including pulse, airflow and air saturation. Together, these tests are called polysomnography. The tests are painless and noninvasive. In-office polysomnography is the gold standard sleep test. Its major drawback is the cost and inconvenience of the study, which is conducted away from home and usually attended by a specially trained technician).

Hoping to make this test more economical, there has been a trend in recent years toward performing a "split" test over the course of a single night. This approach combines a traditional sleep test in the first half of the night with continuous positive airway pressure (CPAP) therapy in the second half of the sleep period. This allows physicians to both confirm a diagnosis and simultaneously calibrate CPAP therapy, which normally requires another night in the sleep clinic.

Because of the cost associated with polysomnography studies, and the increasing frequency of sleep apnea, a number of in-home devices have been designed that allow sleep studies to be conducted while the patient sleeps in his or her own bed. These devices have the obvious advantage of being cheaper and more convenient. However, they tend to measure fewer parameters than in-office equipment, and there is some controversy surrounding the use of in-home technologies versus established sleep center studies.

Currently, researchers are still gathering and analyzing data on the use of portable sleep monitors. So far, these devices are still not recommended to make a stand-alone diagnosis of sleep apnea but can help confirm a diagnosis. In addition, they are not recommended for use in patients with additional conditions, such as obesity or established heart disease.

A multiple sleep latency test (MSLT) may also conducted to record the time it takes for a person to fall asleep in a quiet room during the day. People with sleep apnea can fall asleep within 5 minutes. Normally, a person can fall asleep in 10 to 20 minutes.