Overnight oximetry is a medical test that involves monitoring the level of oxygen in a patient's blood over the course of a night. This test is noninvasive and can be done at home with specialized monitoring equipment. A doctor may recommend it to a patient with disordered sleep to determine if apnea is contributing to the patient's poor sleep patterns. It is an inexpensive test that can provide some important baseline information to determine if a patient needs additional screening, like a sleep study in a hospital or clinic.
In the process of overnight oximetry, the patient puts a small clip on one of the fingers. The clip shines a light through the finger, collecting data about the level of oxygen in the blood by recording the absorption rate of the light as it passes through the finger. It feeds this information to a small recording box via a thin cord. Many patients tape the cord to the hand to keep it from becoming tangled during the night. At the end of the night, the patient can take the clip off, and the overnight oximetry study is complete.
If oxygen levels change during the night, as would be expected if the patient has sleep apnea, the change in readings would show on the data. A doctor can analyze the data from the study to determine if there are any changes. The patient needs to keep a diary that the doctor can compare with the results; if the patient had to move the clip to a different finger, get up to use the bathroom, answer the phone, or engage in other activities, these could skew the results and might create a spike or dip in the oxygen level.
The test results may suggest that the patient's oxygen levels remain stable through the night. In this case, the overnight oximetry indicates that the patient's trouble sleeping is not the result of apnea, and that something else, such as stress, may be causing the problem. If the results show changes in oxygenation levels, the patient may need more testing to address the possibility of apnea and to develop a treatment plan that may help.
Diagnosis of sleep apnea can be a complex process. Overnight oximetry provides a middle point that allows a doctor to collect information at low cost to determine whether a patient appears to have problems with oxygenation during the night. Full sleep studies can be very expensive, and the provision of an alternative test can help cut costs for diagnosis and treatment. Patients may also find the test more pleasant than a sleep study. It is often difficult to sleep in a hospital or clinic, even in rooms designed for sleep studies, and the testing is more intrusive.