Validity of the Leg-O-Meter, an instrument to measure leg circumference

Abstract

The objective of this study was to validate the Leg-O-Meter measure against the clinical assessment of edema made by physicians using data from a 1-year follow-up study of unselected patients with chronic venous disease of the leg (CVDL). The Leg-O-Meter consists of a tape measure fixed to a stand attached to a small board on which the patient is in standing position. Its reliability has been shown to be above 97%. Data from the Venous Insufficiency Epidemiologic and Economic Study (VEINES) were used: 1,521 patients from France, Belgium, Italy, and Quebec (Canada) who spontaneously consulted a physician between 1994 and 1995 with a complaint resulting from venous problems of the legs were included. Baseline variables included leg circumference measurements using the Leg-O-Meter; physicians were also asked to diagnose edema and report it as present or absent on each leg. Clinical edema and leg circumferences were assessed again 3 to 6 months after the baseline visit and 12 months after baseline. The tape measure of the Leg-O-Meter was fixed at 13 cm from the floor. The first and last assessments were used to evaluate the variation in edema during the follow-up period. Clinical variation in edema status was assessed as follows: improved, if edema was diagnosed at baseline but not at the final visit; unchanged, if edema was diagnosed at both visits; and worsened, if there was no diagnosis of edema at baseline but a diagnosis of edema was made at the final visit. Variation in measured edema was classified as improved if there was a decrease in leg circumference of more than 1 cm between baseline and final evaluation; unchanged, if the difference in leg circumference was between plus or minus 1 cm between the 2 assessments; and worsened, if there was an increase in leg circumference greater than 1 cm between the 2 assessments. Data-driven cut-off points were also used: 1.3 cm and 1.5 cm. Sensitivity and specificity of the Leg-O-Meter using physician diagnosis as "gold standard" were calculated. In addition, receiver operating characteristics (ROC) curves were calculated by using the 3 different leg circumference cut-off points in order to determine the accuracy of the Leg-O-Meter to detect changes in edema. The overall accuracy of the Leg-O-Meter was 0.84 (standard error (se) = 0.06). Accuracy was greater when 1.5 cm was used as a cut-point. The Leg-O-Meter is an objective, reliable, and standardized instrument to assess patients over time. A change of 1.5 cm between 2 measurements gives a valid estimate of improvement or worsening of edema, when compared to physicians' diagnosis. The Leg-O-Meter is also sensitive to any changes in leg circumferences, which is an advantage over the clinical evaluation of edema.