Ultrasonographic reference values and a simple yet practical formula for estimating average kidney length in Japanese children

Abstract

Background: The assessment of kidney size is essential for treating kidney disease. However, there are no reliable and sufficiently robust ultrasonographic reference values or prediction formulas for kidney length in Japanese children, based on a sufficient number of participants.

Methods: We retrospectively analyzed kidney measurements by ultrasonography in children aged 18 years or younger from eight facilities throughout Japan between January 1991 and September 2018. Detailed reference values were developed by aggregating the left and right kidneys of boys and girls separately. Simple and practical reference values were developed by combining all the data from left and right kidneys and boys and girls. The estimation formulas for the average value and lower limit of the normal range for kidney length were developed based on regression analysis.

Results: Based on the aggregated kidney length data of 1984 participants (3968 kidneys), detailed reference values and simple reference values for kidney length were determined. From the regression analysis, the formula for calculating the average kidney length was generated as "kidney length (cm) = body height (m) × 5 + 2", and that for predicting the lower limit of normal kidney length in children under 130 cm was calculated as "lower limit (cm) = 0.85 × [body height (m) × 5 + 2]".

Conclusion: Detailed ultrasonographic reference values of kidney length for Japanese children and simple reference values and estimation formulas for daily practice have been established.

Keywords: Chronic kidney disease; Kidney length; Pediatric nephrology; Prediction formula; Reference value; Ultrasonography.

Fig. 1

Participant selection flow chart

Fig. 2

Kidney length by ultrasonography of right (light red cross) and left (light orange cross) kidneys of girls and those of right (light blue cross) and left (light green cross) kidneys of boys according to body height. Colored solid lines show each regression line, and the thick black dashed line indicates the regression line for all participants

Fig. 3

The measured values of kidney length by height by ultrasonography, their regression line (thick dashed line), and the estimated normal values of kidney length (solid line). The straight dotted line shows the lower limit of the normal range by this calculation formula (dotted line). Body height is shown in meters up to 1.3 m

Fig. 4

Kidney length by ultrasonography by body height for five facilities, which reported more than 100 cases. Aichi: Aichi Children’s Health and Medical Center, Nagoya2: Japanese Red Cross Aichi Medical Center Nagoya Daini Hospital, Chiba: National Hospital Organization Chibahigashi National Hospital, NCCHD: National Center for Child Health and Development, Tokyo: Tokyo Metropolitan Children’s Medical Center