FEV1 and "percentages"

[echolaura]

I feel so silly. I have been dealing with my daughter's CF since she was five, and now she's a young adult and at the moment she wants to deal with her doctors appointments herself. We have never been presented with lung function numbers as "percentages", only by FEV1. The way she "does" PFTs now is much different than her previous facility and I am having trouble deciphering the numbers, or even remembering how to reference them. When patients speak of "lung function at 60%, 80, or even OVER 100%, what are they referring to? My daughter's FEV1 only fluctuates by milliliters and is currently 2.1. It has been really difficult for me, she has started going to an adult facility at the SAME TIME as beginning kalydeco (g551d) so I haven't been privvy to her progress, and her health (to me) doesn't seem improved.
Thanks for listening, I appreciate your input, in advance. `frustrated mama.

 

[bcl0328]

I think it's the % predicted divided by actual % or something. Like she blew 2.4 liters and the % predicted would be 3.5. So that 68% function.

 

[Tisha]

There's a theoretical value (based on age, race, weight and length) and there's an actual value. Over the years I've been treated in different hospitals in different countries and thus the theoretical value has been different. The only way for me to compare my values, as I put them all in an Excel spreadsheet a few years ago, was to use the actual value (the real value in liters) and then figure out which theoretical I should apply when calculating the percentage for my own personal usage.

In Europe, they used to work on an "average European" value, which is good for me since my father is Swedish and my mother Spanish, so I'm a mix myself. That theoretical value in my case was 3.10 liters. Lately they went by a Spain-only statistical standard and that one is more demanding (3.25). In turn, Sweden is using a lower value (2.95 I think). So... I blow and I chart my liters and compare in percentage to "my value" (3.10).
Hope this helps!

 

[imported_MaggieB]

The percentage is useful because over the years (for CFers as well as non-CFs) your lungs' volume goes down. And the percentages take your age into account. So when you see that your FEV1 is, say, 60% now, and was 60% ten years ago, you're doing pretty much the same even if the liters has dropped. Does that make sense?

 

[DmT145]

The percentage is useful because over the years (for CFers as well as non-CFs) your lungs' volume goes down. And the percentages take your age into account. So when you see that your FEV1 is, say, 60% now, and was 60% ten years ago, you're doing pretty much the same even if the liters has dropped. Does that make sense?

No, it doesn't. Especially if you grow during that period of time. Basing your lung function on percentage is not wise. As Tisha pointed out, every hospital or country uses different numbers to calculate that percent. Look at the actual numbers and compare them to your last test.

 

[MichaelL]

I don't have much new to add, but I agree that it's better to look at actual numbers. Several years ago my clinic switched the expected value data source from the 1960's to something more current. It appeared my lung function dropped 10%! At that point I started looking at actual numbers. I find the percentages useful if I'm talking to someone not familiar with CF, but use the actual values for myself.

I'm glad to see I'm not the only one who keeps a spreadsheet of my values.

 

[JENNYC]

Me too MichaelL!! I would be lost without my spreadsheets! And like to go by actual numbers too. Good luck mom hope you get it figured out!!

 

[echolaura]

Thank you everybody. I wish my kid would be "lost without her spreadsheets!" Haha! Maybe someday. I'm happy when she just remembers to do Pulmozyme. She's young. Hopefully she will read about all of you and your day to day interest in your own well being. Again, thanks. This means she is running about 63%, which is up from the 40s, prior to initiation of Kalydeco. I will rest. For now.