Variations in FVC and FEV₁ Biologic Quality Control Measures in a Global Multi-Center Clinical Trial

Although quality control standards are recommended to ensure accurate test results, the coefficient of variation for the FVC and FEV₁ biologic quality control (BioQC) is not specified. The primary aim of this study was to evaluate variations in spirometry BioQCs in a large and diverse cohort of individuals to determine an acceptable standard for the coefficient of variation.

The FVC and FEV₁ biologic control data were secondary analyses from an inhaled medication trial that was conducted over 3 y ending in 2018 that included 114 laboratories. Results were sent to a central repository for expert review. The FVC and FEV₁ coefficients of variation were based upon a minimum of 10 spirometry values annually separated by at least 5 d. A second method of computing the coefficient of variation used 10 values within 28 d. Descriptive statistics were computed. Wilcoxon signed-rank tests were conducted to compare whether the median coefficient of variation values between the 2 methods differed, tested at α = 0.05 using SPSS.

Of 249 biologic control participants, 170 met the first year's inclusion criteria. The coefficient of variation for the 5-d separated method was < 5% for 94.1% of FVC and 93.5% of FEV₁ values in the first year. By year 3, 90% of FVC and FEV₁ coefficient of variation values were < 4%. The medians for the 5-d separated and the 28-d measure showed no difference for either FVC coefficient of variation or FEV₁ coefficient of variation, Z = -1.764, P = .78, and Z = -0.980, P = .33, respectively.

Interlab biologic control variation values of < 4% for FVC and FEV₁ are achievable; however, individual labs should strive to attain lower values. Acceptable coefficients of variation can be achieved within 28 d.