AHI and RDI: Why Two Numbers on a Sleep Report Can Differ

A sleep report may give you two different numbers before anyone explains either one. If you are still tired, it can be tempting to decide which number tells the story. Bring both to the interpreting clinician and ask what was counted.

What AHI includes

AHI stands for apnea-hypopnea index. Apneas involve pauses in breathing; hypopneas involve reduced airflow. Hypopnea scoring can include events associated with a brain-recorded arousal or use a rule based on an oxygen drop alone. Ask which rule appears in your report.¹

What RDI adds

RDI stands for respiratory disturbance index. Under the AASM definition, it adds breathing events that lead to arousal without meeting apnea or hypopnea criteria. This explains why the RDI may exceed the AHI on the same study.¹

Ask the clinician to point to the event counts used in the calculation. You do not need to translate every abbreviation before the appointment.

Compare the test as well as the number

Many home sleep apnea tests cannot measure brain-recorded arousals. AASM also distinguishes the home-test respiratory event index, often based on monitoring time, from laboratory indices based on measured sleep time. Those differences matter when interpreting reports.¹

Take the complete report, including the test type and scoring notes, rather than a cropped image of one number. Ask how the findings fit the symptoms that led to testing and what follow-up is recommended.

The Did I Do That in My Sleep? covers snoring and nighttime waking. It offers educational reading alongside the interpretation and care plan supplied by your sleep team. See the book.