Computes the FEV1Q survival index proposed by Miller & Pedersen (ERJ 2010) and discussed as an adult alternative to the conditional change score in Box 3 (p. 13) of the Stanojevic et al. ERJ 2022 interpretation standard. FEV1Q expresses FEV1 in relation to a "bottom line" required for survival, rather than how far an individual's result is from their predicted value; the race-neutral evidence base was consolidated by Balasubramanian et al. (ERJ 2024).
Arguments
- fev1
Numeric vector of FEV1 measurements in litres.
- sex
Character vector of patient sex. Accepts the soft- correctable variants from
pft_spirometry()("Male","female", etc.); unrecognized values yieldNA.- age
Optional numeric vector. When supplied, rows with
age < 18returnNA_real_per the paper's "not appropriate for children and adolescents" caveat. DefaultNA_real_skips the guard.
Details
Formula (Box 3 verbatim): $$FEV1Q = FEV1 / Q_{sex}$$
where \(Q_{male} = 0.5 L\) and \(Q_{female} = 0.4 L\) are the sex-specific 1st percentiles of the FEV1 distribution in adult lung-disease populations. The index approximates the number of turnovers remaining of a lower survivable limit of FEV1; values closer to 1 indicate greater risk of death.
The 2022 standard cautions (running text on p. 13, immediately
preceding Box 3): "FEV1Q is not appropriate for children and
adolescents." When age is supplied,
rows with age < 18 return NA_real_. When age is omitted, the
age guard is skipped and the caller is responsible for restricting
input to adults.
For longitudinal interpretation in adults the 2022 standard
suggests FEV1Q as an alternative to the conditional change score
(see pft_change()): under normal circumstances 1 unit of FEV1Q is
lost approximately every 18 years (every ~10 years in smokers and
the elderly).
References
Miller MR, Pedersen OF. New concepts for expressing forced expiratory volume in 1 s arising from survival analysis. Eur Respir J. 2010;35(4):873-882. doi:10.1183/09031936.00025809 . Original proposal of the FEV1Q index and the sex-specific 1st-percentile denominators (0.5 L male, 0.4 L female).
Balasubramanian A, Wise RA, Stanojevic S, Miller MR, McCormack MC. FEV1Q: a race-neutral approach to assessing lung function. Eur Respir J. 2024;63(4):2301622. doi:10.1183/13993003.01622-2023 . Race-neutral validation of the FEV1Q index.
Stanojevic S, Kaminsky DA, Miller MR, et al. ERS/ATS technical standard on interpretive strategies for routine lung function tests. Eur Respir J. 2022;60(1):2101499. doi:10.1183/13993003.01499-2021 . Discusses FEV1Q in Box 3 (p. 13) as an adult alternative to the conditional change score.
See also
pft_change() for the conditional change score (the
children / young-people sibling); pft_severity() for the
z-score-based severity grading.
Examples
# Stanojevic 2022 Box 3 worked example: a 70-year-old woman with
# FEV1 of 0.9 L has FEV1Q of 0.9 / 0.4 = 2.25.
pft_fev1q(0.9, "F", age = 70)
#> [1] 2.25
# Vectorised across sex.
pft_fev1q(c(1.0, 1.0), c("M", "F"))
#> [1] 2.0 2.5
# Adolescents return NA when age is supplied.
pft_fev1q(1.0, "F", age = 10)
#> [1] NA