The Impact of Using Non-Birth Sex on the Interpretation of Spirometry Data in Subjects With Air-Flow Obstruction.

BACKGROUND: Sex is an important determinant of lung capacity and function. This study examined the impact of using non-birth sex on the interpretation of spirometry data in transgender subjects with air-flow obstruction.

METHODS: This study was a retrospective analysis of anonymous spirometry data. Eighty adult male and 80 adult female subjects were chosen from the database via random sampling. FVC, FEV1 , and FEV1 /FVC were collected and analyzed. Differences in percent of predicted, Z scores, classification of disease severity, and the incidence of a value migrating above or below the lower limit of normal between sex assignments were examined.

RESULTS: For born male subjects, percent of predicted for FVC and FEV1 were significantly higher when the female sex was used: 100.5% versus 118.5% and 78% versus 91.5%, respectively ( P < .001). FEV1 /FVC Z score was -2.53 for male sex and -2.65 for female sex ( P = .004). The presence of obstruction was not affected by sex assignment. Use of non-birth sex moved some FVC and FEV1 data above the lower limit of normal and improved severity classification in others. For born female subjects, percent of predicted for FVC and FEV1 were significantly lower when the male sex was used: 102% versus 87.5% and 81.5% versus 70.5%, respectively ( P < .001). FEV1 /FVC Z score was -2.17 for female sex and -2.12 for male sex ( P < .001). Six born female subjects had their FEV1 /FVC normalized when male sex was used. Use of non-birth sex moved some FVC and FEV1 data below the lower limit of normal and worsened severity classification in others. In total, using the non-birth sex affected spirometry interpretation in 45% of born male subjects and 70% of born female subjects.

CONCLUSIONS: In transgender subjects with air-flow obstruction, using non-birth sex to calculate predicted spirometry values may have a significant impact on test interpretation and place these patients at risk for misdiagnosis and inappropriate treatment.