An investigation into the accuracy and test-retest reliability of the perometer compared to a water displacement method for measuring lower limb volume in healthy human participants.

Abstract

Aim: To investigate the accuracy and test-retest reliability of the perometer compared to a water displacement method for measuring lower limb volume in healthy human participants. Design: Between-methods agreement and test-retest reliability study. Participants: 15 healthy volunteers (8 females and 7 males) with no drop-outs. Intervention: All participants had their dominant lower limb volumes measured using both the vertically-oriented perometer and volumeter. Allocation to either tests was random and in no specific order, but both tests had to be completed. Outcome measures: ICC(3,1) model was used to determine the test-retest reliability for each method, while the measurement error was determined using within-subject standard deviation. A one sample t-test was used to determine the accuracy of the vertically-oriented perometer compared to the volumeter, while a Bland and Altman difference plot was constructed to determine the limits of agreement between both methods. Results: There was a lack of agreement between the perometer and water displacement method. The Bland-Altman difference plot showed that the perometer overestimated lower limb volume by 832ml compared to the water displacement method. The respective upper and lower limits of agreement were 220 and 1444ml. The test-retest reliability of the perometer method was ICC(3,1)=0.994. The measurement error of the perometer method was clinically acceptable (149ml). Conclusion: There was a lack of agreement between the two methods investigated. Therefore, the perometer and water displacement methods are not interchangeable. It is recommended that future validity and reliability studies for the vertically-oriented perometer are conducted on an older and clinical population.