How Do They Calculate AHI?

Another chapter in my education.

"They" say that to calculate the AHI, you add the number of SA, OA and hypopneas over the sleep period and divide by the number of sleep minutes.

But the individual indices -- CA, OA, hypop, and RERA -- are calculated the same way.

Since each index was calculated using the same denominator, I should be able to simply add all the indices (except RERA) to get AHI.

However, my reports show Avg CA Index/avg OA Index/avg hypop Index/avg RERA index/AHI as follows over the period of several days:

Overall: 2.1/3.9/5.5/10.7/11.5
1.3/4.1/6.3/13.5/11.7
1.5/6.3/7.8/15.4/15.6
1.5/5.1/8.2/10.5/14.9
21./3.4/4.7/13.9/10.2

Where is my thinking off????

Thanks.

It appears that your numbers add up just the way they should with a rounding error of +/- 0.1

Overall: 2.1/3.9/5.5/10.7/11.5----- 2.1+3.9+5.5=11.5
1.3/4.1/6.3/13.5/11.7--------------- 1.3+4.1+6.3=11.7
1.5/6.3/7.8/15.4/15.6 -------------- 1.5+6.3+7.8=15.6
1.5/5.1/8.2/10.5/14.9--------------- 1.5+5.1+8.2=14.8
21./3.4/4.7/13.9/10.2--------------- 2.1+3.4+4.7=10.2

Did you forget and add in reras even after you mentioned omitting them above?

RERAs are NOT part of the AHI number.

You can figure AHI 2 ways...
Take the total number of events (CA, OA & Hyponea) and divide by number of hours of sleep (or do minutes and divide by 60).

Or you can take each of the hourly indices for each category shown on the report and add them together.

Both will come up with AHI which is the hourly index for all events that are counted. RERA is not counted in AHI.
Some docs will count RERA in a RDI...Respiratory Disturbance Index.