Interpreting the Respiratory Event Index and Oxygen Desaturation Metrics in Home Sleep Apnea Diagnostic Reports
Upon completion of a Home Sleep Apnea Test, the raw data is uploaded into specialized software for analysis. The resulting report contains several critical indices that define the presence and severity of the condition.
The most important metric is the Respiratory Event Index (REI). While similar to the AHI, the REI is calculated by dividing the total number of respiratory events (apneas and hypopneas) by the total monitoring time.
Normal: REI < 5 events per hour.
Mild OSA: REI 5 to 14.9 events per hour.
Moderate OSA: REI 15 to 29.9 events per hour.
Severe OSA: REI ≥ 30 events per hour.
In addition to the frequency of events, the Oxygen Desaturation Index (ODI) is scrutinized. This measures how many times per hour the blood oxygen levels drop below a certain threshold (usually a 3% or 4% decrease from the baseline). A patient might have a moderate REI but a severe ODI, suggesting that while their breathing pauses aren't as frequent, the impact on their blood chemistry is profound.
The report also examines Body Position. Many patients suffer from "Positional OSA," where events occur predominantly when they are lying on their back. The HSAT device usually includes an internal gyroscope to track whether the patient is supine, prone, or on their side. If the report shows that the REI is 30 while supine but only 4 while on the side, the clinician might recommend "positional therapy" as a primary or adjunctive treatment.