Observer Variability in Sonographic Measurement of Kidney Sizes among Children in Benin-City, Nigeria

To assess the level of inconsistency in replicating sonographic kidney size measurements in a population of healthy Nigerian children.

In this prospective cross-sectional study, convenience sampling technique was used to select a sample of Nigerian children. Both consent from participants and ethical approval from the local authority were obtained before the study commenced. Three radiologists carried out the replicate sonographic measurements using a DP-1100 mechanical sector scanner with a 3.5 MHz convex probe. All examinations were done with subjects in the supine oblique position. Longitudinal and transverse scans were performed. Renal lengths and widths were measured from the longitudinal scans while thickness was measured from the transverse scans. Renal volumes were calculated with the ellipsoid formula. Analysis of variance, Student's t-test, Pearson's correlation coefficient and z-test were used to test the statistical significance of results. SPSS version 17.0 was used in the analysis of results while statistical significance of all results was tested at p < 0.05.

Mean intra-observer measurement errors in replicate sonographic measurements of kidney sizes ranged from 0.36-0.43 cm, 0.22-0.63 cm, 0.37-0.52 cm and 5.93-9.62 ml for kidney length, width, thickness and volume, respectively. Mean inter-observer measurement errors were in the range of 0.29-0.48 cm, 0.18-0.23 cm, 0.34-1.82 cm and 5.92-7.28 ml for length, width, thickness and volume, respectively. Mean intra-observer errors were not statistically significant (p < 0.05) but mean inter-observer errors were (p < 0.05). Differences in all measurement errors of right and left kidney length, width, thickness and volume were not statistically significant (p > 0.05). Measurement errors correlated weakly with kidney sizes. Observer errors in renal length were not significantly different from what was reported among Caucasians (p > 0.05) whereas that of volume was (p < 0.05).

Errors in replicate sonographic kidney size measurements obtained by a single observer were less than errors in the same measurements by different observers; therefore, replicate sonographic measurements by a single observer were more consistent in this population.