Table 2– Paediatric reference equations for lung clearance index (LCI) and functional residual capacity (FRC) measured by multiple-breath washout (MBW)
LCI
L-0.81
 Predicted M5.99 + (73.85 × height−1)
S0.08
 ULNPredicted × ((1.96 × 0.08 × -0.81) + 1)1/-0.81
FRCMBW
L0.21
 Predicted Mexp (-11.07 + (2.12 × ln height) + (0.27 × age0.5) + (0.04 × sex))
Sexp (-1.67 + 159.61 × height−2)
 ULNPredicted × ((1.96 × S × 0.21) + 1)1/0.21
  • Based on these equations, the upper limit of normal (ULN) for LCI can be simplified to predicted LCI × 1.18, whereas that for FRCMBW becomes (0.36 × S + 1)5.37 × predicted FRCMBW. For simplicity, the factors are displayed to two decimal places. For calculation of z-scores and the ULN, the full equations presented in table S3 should be used. L: lambda (skewness); M: mu (mean); S: sigma (coefficient of variation); height: height in cm; age: age in years; sex: female = 0, male = 1.