Grade severity of lung function impairment from a z-score

Assigns one of four severity categories ("normal", "mild", "moderate", "severe") to a z-score per the Stanojevic et al. ERS/ATS 2022 interpretation standard. The same grading applies uniformly to spirometry, lung-volume, and diffusion measures.

Boundary conventions (matching the function's implementation):

Grade	z-score
normal	z >= -1.645
mild	-2.5 <= z < -1.645
moderate	-4 <= z < -2.5
severe	z < -4

Usage

pft_severity(zscore)

Arguments

zscore

Numeric vector of z-scores.

Value

Character vector the same length as zscore with values "normal", "mild", "moderate", "severe", or NA.

References

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 . The cut points are taken from the "Severity of lung function impairment" section.

See also

pft_classify() for the pattern label that severity sits alongside; pft_gold() for COPD-specific severity from FEV1 percent predicted; pft_interpret() applies this grading to every z-score column in one call.

Examples

pft_severity(c(0, -1.7, -3, -5))
#> [1] "normal"   "mild"     "moderate" "severe"  
# -> "normal" "mild" "moderate" "severe"