The reliability of ultrasonographic measurements for testicular volume assessment: comparison of three common formulas with true testicular volume

Abstract

The aim of this study was to determine the correlation of ultrasonographic estimates of testicular volume with true testicular volume and to compare the accuracy and precision of the three most commonly utilized formulas. A total of 15 patients underwent high-resolution ultrasonography (US) analysis for testicular volume before orchiectomy. Testicular volume was calculated using three common formulas: (1) length (L) x width (W) x height (H) x 0.52; (2) the empirical formula of Lambert: L x W x H x 0.71; and (3) L x W2 x 0.52. The actual volume of each removed testis was estimated directly by a water displacement method. Thus, four volume measurements were obtained for each of the 30 testes. The obtained data were analyzed by paired t-test and linear regression analysis. All three US formula measurements significantly underestimated the true testicular volume. The largest mean biases were observed with US formula 1, which underestimated the true volume by 3.3 mL (31%). US formula 2 had a smaller mean difference from the true volume, with an underestimation of only 0.6 mL (6%). Regression analysis showed that formulas 1 and 2 had better R2 values than formula 3. However, all three US formulas displayed a strong linear relationship with the true volume (R2= 0.872-0.977; P < 0.001). Among the commonly used US formulas, the empirical formula of Lambert (L x W x H x 0.71) provided better accuracy than the other two formulas evaluated, and better precision than formula 3. Therefore, the formula of Lambert is the optimal choice in clinical practice.

Figure 1

Testicular volume assessed by ultrasonography. (A): The largest length (L) and height (H) in the longitudinal plane were measured using electronic calipers. (B): Adequate width (W) in the transverse plane was also obtained using calipers.

Figure 2

The linear relationship between actual testicular volumes and volumes determined by different formulae. The straight, dashed lines represent the theoretical linear relationship obtained from regression parameters. The curved, dashed lines represent the 95% confidence intervals. Formula 1 = length (L) × width (W) × height (H) × 0.52, Formula 2 = L × W × H × 0.71, and Formula 3 = L × W² × 0.52. Although all three formulae tended to underestimate the testicular volume, formula 2 resulted in values that differed the least from the actual volume.