Concurrent validity of upper-extremity volume estimates: comparison of calculated volume derived from girth measurements and water displacement volume.

BACKGROUND AND
PURPOSE: The volume of all limbs can be determined by water displacement methods or calculations derived from girth measurements. The purpose of this study was to determine the concurrent validity of calculated volume and water displacement volume measurements.
SUBJECTS: Both upper extremities of 14 women with lymphedema were measured.
METHODS: Volumetric measurements were taken with a volumeter, and circumferential measurements were taken with a tape measure. Calculated volume was determined by summing segment volumes derived from the truncated cone formula. Pearson product moment correlations, paired t tests, and linear regression tests were used to assess relative association and absolute differences between calculated and actual volumes.
RESULTS: The correlation coefficient for calculated volume versus upper extremity minus fingers (UE-F) water displacement volume was.99. Paired t tests showed differences between calculated volume and UE-F water displacement volume (t=-3.88, mean difference=-95.62 mL), and the linear regression slope was 0.83 with an intercept of 255.28 mL. DISCUSSION AND
CONCLUSION: Calculated volume measurements were highly associated with measurements based on water displacement; therefore, clinicians should feel confident in using either calculated volume or water displacement volume. The differences, however, indicated that the measures were not interchangeable. Thus, clinicians should not mix or substitute measurement methods with a single patient or in a single study.