Background

Blood eosinophil counts (BEC) are elevated in a subgroup of COPD patients. Higher BEC demonstrate greater temporal variability in COPD. Variability of BEC in smokers at risk of developing COPD is currently unknown.

Methods

BEC were obtained at baseline and 6 months from younger smokers (S) (NCT03480347). Subjects were aged <45 years, with a pack year history of ? 10 and normal FEV₁ (>80%). At baseline, 534 BEC were obtained, with 266 repeat counts at 6 months. Low, intermediate and high BEC were defined by thresholds of <100, 100-300 and >300 cells/µL respectively.

Results
Median baseline BEC was 180cells/µL, with low, intermediate and high groups represented by 10, 76 and 14% of S respectively (n=534). A good correlation was observed between repeated BEC (r=0.65, p<0.0001, Figure 1A, n=266), with ICC= 0.79. Intermediate BEC were most stable, with 90% remaining in the same category upon repeat testing, in comparison to low and high groups; 52 and 47% remained stable respectively (Figure 1B, C & D). Bland-Altman analysis revealed greater variability at higher BEC (mean difference: 2.29, LOA: -203.7 - 208.3 cells/µL).

Figure 1: Association between repeat BEC (A), baseline and 6-month measures of BEC for low (B), intermediate (C) and high (D) groups. n=266.

Conclusion

We demonstrate excellent overall short-term stability of BEC in S, with the greatest temporal variability observed in those with BEC >300 cells/µL.