ESPE Abstracts

Background: Prader orchidometry has been the standard method for evaluating testicular size. As this technique is subjective and tends to overestimate the testicular volume, ultrasound has been proposed as a more reliable method.

Objective: To evaluate the intra- and inter-observer agreement of ultrasound measurements of testicular volume and comparison with Prader orchidometry.

Materials and methods: Length, width and depth of the right testicle were measured using ultrasound in 57 boys between 6.5 and 16.4 (mean 12.0) years of age. Volume calculated by Lamberts formula: L×W×D×0.71. The measurements were performed twice by a main observer and once by a second observer. Testicular volume was also estimated using a Prader orchidometer by a third observer. Agreement was investigated with Bland-Altman plots, and summarized as the mean and S.D. of differences, 95% limits of agreement (LOA), and technical error of measurement (TEM).

Results: The mean intra-observer difference of testicular volume was 2.2% with an SD of 9.2% (LOA −20.3 to 15.9%) and TEM of 6.5%. The mean inter-observer difference was 4.8% with an SD of 20.7% (LOA −35.7 to 45.3%) and TEM of 14.6%. Comparing ultrasound and orchidometer volumes required a power transformation to remove bias, estimated as Vol_OM=1.96*Vol_US^0.71. The mean difference after transformation was 0.7% with an SD of 18.0% (LOA from −34.5 to 35.9%).

Conclusion: Our results showed a relatively small mean intra- and inter-observer difference that indicates the potential of ultrasound for measurement of testicular volume on a group level. The intra-observer error was limited which justifies its use in longitudinal follow up of testicular development in an individual child, but the larger inter-observer variability indicates the need for good standardization of methods. Agreement between the two methods required a power transformation to remove bias.

Keywords: agreement, intra-observer, inter-observer, testicular volume, ultrasound, orchidometer