COPD and the FEV1/FVC ratio. GOLD or LLN?

Everyone uses the FEV1/FVC ratio as the primary factor in determining the presence or absence of airway obstruction but there are differences of opinion about what value of FEV1/FVC should be used for this purpose. Currently there are two main schools of thought; those that advocate the use the GOLD fixed 70% ratio and those that instead advocate the use the lower limit of normal (LLN) for the FEV1/FVC ratio.

The Global Initiative for Chronic Obstructive Lung Disease (GOLD) has stated that a post-bronchodilator FEV1/FVC ratio less than 70% should be used to indicate the presence of airway obstruction and this is applied to individuals of all ages, genders, heights and ethnicities. The official GOLD protocol was first released in the early 2000’s and was initially (although not currently) seconded by both the ATS and ERS. The choice of 70% is partly happenstance since it was one of two fixed FEV1/FVC ratio thresholds in common use at the time (the other was 75%) and partly arbitrary (after all why not 69% or 71% or ??).

The limitations of using a fixed 70% ratio were recognized relatively early. In particular it has long been noted that the FEV1/FVC ratio declines normally with increasing age and is also inversely proportional to height. For these reasons the 70% threshold tends to over-diagnose COPD in the tall and elderly and under-diagnose airway obstruction in the short and young. Opponents of the GOLD protocol say that the age-adjusted (and sometimes height-adjusted) LLN for the FEV1/FVC ratio overcomes these obstacles.

Proponents of the GOLD protocol acknowledge the limitation of the 70% ratio when it is applied to individuals of different ages but state that the use of a simple ratio that is easy to remember means that more individuals are assessed for COPD than would be otherwise. They point to other physiological threshold values (such as for blood pressure or blood sugar levels) that are also understood to have limitations, yet remain in widespread use. They also state that it makes it easier to compare results and prevalence statistics from different studies. In addition at least two studies have shown that there is a higher mortality of all individuals with an FEV1/FVC ratio below 70% regardless of whether or not they were below the FEV1/FVC LLN. Another study noted that in a large study population individuals with an FEV1/FVC ratio below 70% but above the LLN had a greater degree of emphysema and more gas trapping (as measured by CT scan), and more follow-up exacerbations than those below the LLN but above the 70% threshold.

Since many of the LLN versus GOLD arguments are based on statistics it would be useful to look at the predicted FEV1/FVC ratios in order to get a sense of how much under- and over-estimation occurs with the 70% ratio. For this reason I graphed the predicted FEV1/FVC ratio from 54 different reference equations for both genders and a variety of ethnicities. Since a number of PFT textbooks have stated that the FEV1/FVC ratio is relatively well preserved across different populations what I initially expected to see was a clustering of the predicted values. What I saw instead was an exceptionally broad spread of values.




Looking closely I am unable to see any particular relationship between ethnicity or geographical location and the FEV1/FVC ratio. This fact is highlighted by the slope (rate of decline) of the FEV1/FVC ratios with age.



Many of the studies that were the source of these reference equations did not include an LLN specifically for the FEV1/FVC ratio. For this reason I used 90% of predicted as a conservative substitute (this decision is based on the NHANESIII FEV1/FVC ratio LLN that is approximately 89%-90% of the predicted across the range of ages for all ethnicities).



When this is done, the limitation of the 70% ratio in relation to increased age becomes more obvious, particularly since the average of all LLN’s (for males) reaches 70% at age 65. This means that approximately half of the reference equation LLN’s show a decrease below 70% before that age, and some as young as age 33. Theoretically at least, using the GOLD criteria by age 65 up to half of the world population could have spirometry that was potentially within normal limits but would be considered to have COPD.

At first glance this is a strong argument in favor of the use of the LLN to determine the presence of airway obstruction, and in general I would agree. However, what it also makes quite clear is that the LLN is highly dependent on which reference equation is chosen and this to some extent bolsters the pro-GOLD argument about its simplicity.

I was surprised at the wide range of values from the different reference equations particularly since the FEV1/FVC ratio is often considered to be a highly conserved value between ethnicities (and notably within the NHANESIII and GLI studies there is little difference between Blacks, Hispanics, Caucasians and Asians). The reasons for this wide range of results are unclear and may be related to differences in the size or makeup of the different study populations, differences in statistical analysis and/or differences in the spirometry equipment. It should also be noted that the criteria used to assess test quality and the acceptability of spirometry results are based on the individual characteristics of the FVC and FEV1, not on the FEV1/FVC ratio.

The ATS/ERS statement on interpretation recommends the use of the largest vital capacity, regardless of source, when calculating the FEV1/FVC ratio. The effect that this has on the prevalence of airway obstruction by either the LLN or 70% threshold does not appear to have been explored, however. Using the reference equations from Gutierrez et al (chosen because the same population was used to derive reference equations for both spirometry and lung volumes) it appears that the FEV1/SVC ratio is lower than the FEV1/FVC ratio at all ages and that the difference between the two increases as age increases.


Although I fully understand and agree with the point of using the SVC when it is larger than the FVC, this makes it clear that the LLN for the FEV1/FVC ratio does not apply to the FEV1/SVC ratio.

Conversely, the FEV1/FEV6 has less variability than the FEV1/FVC ratio and for this reason has been suggested as a more reliable substitute. FEV6 however, can also be reduced when obstruction is present and for this reason the decrease in the FEV1/FEV6 ratio may not be a reliable indicator of the severity of obstruction.

The GOLD criteria were developed primarily to diagnose the presence of COPD. One of the hallmarks of COPD is that it is only minimally responsive to short-acting bronchodilators. For this reason at least some of the confusion surrounding the GOLD 70% threshold lies in the fact that it should only be applied to the post-bronchodilator FEV1/FVC ratio. It has been shown that the number of individuals considered to have airway obstruction using the GOLD criteria increases by up to 30 percent when only the pre-bronchodilator FEV1/FVC ratio is considered. This doesn’t necessarily make the 70% threshold more correct but it also shouldn’t be applied as a general rule to all spirometry either.

One criticism that I’d level at a number of the papers advocating the use of the LLN over the GOLD 70% threshold is that the authors often begin by defining airway obstruction as an FEV1/FVC ratio below the LLN and then proceed to critique the 70% threshold for mis-categorizing individuals. I don’t necessarily disagree with the underlying premise but this approach is a little specious since at least one study has indicated that the use of the LLN alone tends to under-diagnose COPD. Other studies have indicated that the addition of a reduced FEV1 (either below 80% of predicted or the LLN) and an elevated RV/TLC ratio are needed in addition to an FEV1/FVC below the LLN in order to improve specificity.

There is some evidence that individuals with an FEV1/FVC ratio below 70% tend to have more significant lung disease and a higher mortality. Numerous studies however, have shown that the GOLD threshold overestimates airway obstruction in the elderly and the tall and underestimates it in the young and the short. The predicted FEV1/FVC ratio LLN’s largely agree with this finding. I think that the greatest fault of the GOLD 70% threshold is that for too many individuals it confuses the normal changes that occur as part of aging with a disease process. Since an incorrect diagnosis of COPD can lead to inappropriate care plans, testing and medications for a patient, this alone probably outweighs any advantages the 70% threshold may have.

The preponderance of evidence is in favor of the FEV1/FVC ratio LLN. Moreover it is applicable to all forms of airway obstruction which includes pre-bronchodilator spirometry and this generally makes it more useful than the 70% threshold, particularly for the young. The LLN approach is not without its own problems, however, and any diagnosis of COPD should be multifactorial and rely on more than just the FEV1/FVC ratio. In addition more than one study has noted that which patients are considered to have airway obstruction was dependent on which set of reference equations were used for analysis and as can be seen the differences between reference equations, even within the same ethnicities, can be quite large.

Part of the problem with either approach is that most patients being screened for COPD are often performing spirometry for the first time in their lives. Without any knowledge of an individual’s baseline results the quality of any diagnosis is necissarily going to be limited. A simple answer to this is that spirometry, like blood pressure, needs to become a more commonly performed test, most particularly for patients that for whatever reason (smoking, work exposure, elevated air pollution, genes) have a higher level of risk.

The broad spread in the FEV1/FVC ratio reference equations is a problem for both the 70% threshold and the LLN. For the 70% threshold it puts into question both whether the FEV1/FVC ratio is actually preserved across different population and moreover whether 70% itself is correct. For the LLN, it may well be true that the LLN is more statistically correct, but the selection of the most appropriate reference equations for any one individual remains problematic.

FEV1/FVC Ratio Reference Equations, Study characteristics:

Ethnicity: #Female: Female Ages: #Male: Male Ages:
[A] Saudi 292 18-65 175 18-65
[B] Ethiopian Jewish 45 25-70 47 25-70
[C] Hispanic 143 20-80 116 25-75
[D] Asian Indian 137 20-80 226 16-80
[E] Iranian 1110 21-80 1302 21-80
[F] White 327 20-79 300 20-79
[G] White 927 21-80 476 21-80
[G] Black 772 21-80 422 21-80
[G] Hispanic 872 21-80 506 21-80
[H] Chinese 595 18-80 494 18-80
[I] Northern Indian 540 15-74 422 15-74
[J] White 1129 27-82 1106 27-82
[K] White 176 20-69 86 25-70
[L] White 7009 18-80 4565 18-80
[M] Chinese 0 440 18-80
[N] American Indian 253 45-74 190 45-74
[O] White 102 18-70 110 18-70
[P] Black 117 18-47 143 18-47
[Q] White 471 20-84 517 20-84
[R] White 97 Not stated 102 Not stated
[S] Korean 694 20+ 926 20+
[T] White 270 25 to >75 373 20 to >75
[U] Iranian 255 17-82 295 17-82
[V] Filipino 153 16-68 130 17-78
[W] White 96 18 to >70 83 18 to >70
[X] Malaysian 614 20-69 1385 20-69
[Y] Jewish-Ashkenazi 663 20-74 1154 21-79
[Y] Jewish-Sephardic 547 20-69 786 21-84

FEV1/FVC Ratio Reference Equations, Direct

Male: FEV1/FVC Ratio:
[A] Saudi (-0.068*Height)-(0.095*Age)+98.41
[C] Hispanic 86.5881-(0.116*Age)
[E] Iranian (-0.0978*Height)-(0.104*Age)+107.21
[F] White 109.396-(0.113*Height)-(0.21*Age)
[G] White 88.066-(0.2066*Age)
[G] Black 89.239-(0.1828*Age)
[G] Hispanic 90.024-(0.2248*Age)
[I] Northern Indian 103-(0.35*Age)+(0.002*Age^2)-(0.07*Height)
[L] White EXP(6.291-(0.341*LN(Height))-(0.00441*Age)+(0.000026*Age^2))
[M] Chinese 112.75058-(0.25439*Age)-(0.1181*Height)
[N] American Indian (-0.328*Age)+94.789
[O] White 108.1-(0.24*Age)-(10.6*(Height/100))
[T] White (-0.175*Height)-(0.197*Age)+120.3
[W] White (-21.476*(Height/100))-(0.242*Age)+126.252
[Y] Jewish-Ashkenazi 111.77-(0.123*Age)-(14.295*(Height/100))
[Y] Jewish-Sephardic 99.09-(0.123*Age)-(6.57*(Height/100))
Female: FEV1/FVC Ratio:
[A] Saudi (-0.072*Height)-(0.142*Age)+100.67
[C] Hispanic 91.7259-(0.1862*Age)
[E] Iranian (-0.133248*Height)-(0.084349*Age)+112.1081
[F] White 104.509-(0.089*Height)-(0.182*Age)
[G] White 90.809-(0.2186*Age)
[G] Black 91.229-(0.2039*Age)
[G] Hispanic 92.36-(0.2248*Age)
[I] Northern Indian 111-(0.36*Age)+(0.003*Age^2)-(0.1*Height)
[L] White EXP(5.637-(0.219*LN(Height))-(0.00249*Age)+(0.000004*Age^2))
[N] American Indian (-0.1967*Age)+89.565
[O] White 108.1-(0.24*Age)-(10.6*(Height/100))
[T] White (-0.14*Height)-(0.158*Age)+111.5
[W] White (-0.172*Age)+88.134
[Y] Jewish-Ashkenazi 111.77-(0.123*Age)-(14.295*(Height/100))
[Y] Jewish-Sephardic 99.09-(0.123*Age)-(6.57*(Height/100))

FEV1/FVC Ratio Reference Equations, Indirect

Male: FEV1: FVC:
[B] Ethiopian Jewish (2.26*(Height/100))-(0.0221*Age)-0.0593 (3.994*(Height/100)-(0.0234*Age)-2.507))
[D] Asian Indian -1.936+(0.035*Height)-(0.026*Age) -2.754+(0.043*Height)+(-0.024*Age))
[H] Chinese -2.404-(0.0254*Age)+(0.03978*Height) -4.424-(0.0193*Age)+(0.05434*Height))
[J] White -4.261-(0.0296*Age)+(5.465*(Height/100)) -6.142-(0.0281*Age)+(7*(Height/100)))
[K] White -6.5147+(0.0665*Height)-(0.0292*Age) -8.7818+(0.0844*Height)-(0.0298*Age))
[P] Black -3.6679-(0.0331*Age)+(0.0501*Height) -6.839-(0.0195*Age)+(0.0695*Height))
[Q] White (0.092*(Height/2.54))-(0.032*Age)-1.26 (0.148*(Height/2.54))-(0.025*Age)-4.241)
[R] White (0.092*(Height/2.54))-(0.032*Age)-1.26 (0.138*(Height/2.54))-(0.027*Age)-3.445)
[S] Korean (0.04578*Height)-(0.0002484*Age^2)-3.4132 (0.05292*Height)+(0.010947*80)-(0.00008633*Age^2)-4.8434)
[U] Iranian (0.043822*Height)-(0.028801*Age)-2.425 (0.062271*Height)-(0.027131*Age)-5.086)
[V] Filipino -3.2068+(0.0436*Height)-(0.0205*Age) -4.4496+(0.0526*Height)-(0.0099*Age))
[X] Malaysian (0.0353*Height)-(0.0315*Age)-1.78 (0.0407*Height)-(0.0296*Age)-2.343)
Female: FEV1: FVC:
[D] Asian Indian -0.401+(0.021*Height)-(0.021*Age) -0.842+(0.027*Height)-(0.02*Age))
[H] Chinese -1.272-(0.0199*Age)+(0.02825*Height) -2.697-(0.0149*Age)+(0.03894*Height))
[J] White -1.747-(0.0263*Age)+(3.619*(Height/100) -4.04-(0.0259*Age)+(5.364*(Height/100)))
[K] White -1.405+(0.0309*Height)-(0.0201*Age) -2.9001+(0.0427*Height)-(0.0174*Age))
[P] Black -1.6158-(0.0178*Age)+(0.0298*Height) ((-2.9208-(0.0122*Age)+(0.0407*Height))))*100
[Q] White (0.089*(Height/2.54))-(0.025*Age)-1.932 -3.335+(0.049*Height)-(0.024*Age))*100
[R] White (0.085*(Height/2.54))-(0.025*Age)-1.692 (0.114*(Height/2.54))-(0.024*Age)-2.795)
[S] Korean (0.03558*Height)-(0.000192*Age^2)-2.4114 (0.03951*Height)+(0.006892*65)-(0.00012728*Age^2)-3.0006)
[U] Iranian (0.039489*Height)-(0.023593*Age)-2.498 (0.046167*Height)-(0.022557*Age)-3.274)
[V] Filipino -1.0375+(0.0256*Height)-(0.0187*Age) -1.4297+(0.0302*Height)-(0.0159*Age))
[X] Malaysian (0.0294*Height)-(0.0238*Age)-1.609 (0.0312*Height)-(0.022*Age)-1.64)


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