Reliability and concurrent validity of the perometer for measuring hand volume in women with and without lymphedema

Background: Lymphedema of hand after breast cancer treatment causes significant loss of hand function. Although there are several ways of assessing limb volume, measuring hand volume has been problematic due to technical difficulties associated with assessment of finger volumes. The aim of this study was to investigate the criterion validity and reliability of Perometer™ for measuring hand volume in woman with and without lymphedema. Methods and Results: Hand volume of forty women with (n=20) and without lymphedema (n=20) was assessed twice by one rater and once by another rater using the Perometer, and once by one rater using the water volumetry method. Intra- and inter-rater reliability was determined from the intraclass correlation coefficients and Percent Close Agreement. Agreement between the Perometer and water volumetry was determined using a limit of agreement and Lin's concordance correlation. The Perometer had high intra [ICC_2,1=0.989 (95% CI: 0.98-0.99)] and inter-rater reliability [ICC_2,1=0.993 (95% CI: 0.99-1.0)]. Percent close agreement revealed that 80% of the measures were within 9ml for inter-rater reliability and within 15ml for intra-rater reliability. In addition, there was high concordance between hand volumes obtained with the Perometer and water volumetry method (R_c=0.88). However, the Perometer overestimated the volume of hand compared to water volumetry method (bias: 7.5%). Conclusions: The Perometer can be used with high reliability to measure hand volume but caution should be exercised when data are compared with measures derived from the water volumetry method.