The effect of fluid intake on renal length measurement in adults

To evaluate whether oral fluid intake has an effect on renal length as determined with sonography.

We studied 524 adult patients who were referred to our ultrasound unit with complaints other than urinary tract symptoms. The mean age of the patients was 44 years (range 17-76). All of the measurements were performed with the patient in the prone position. The renal length of each kidney was measured by the same observer before and after oral fluid intake. Student's t-test was applied for the statistical significance of renal length measurements before and after hydration. Analysis of variance was performed for the effect of age and sex on the renal length measurements.

The mean renal length on the right side was 106.2 +/- 5.5 mm and 107.5 +/- 5.7 mm on the left side before hydration. There was no statistically significant difference between right and left side renal length measurements. After hydration, the mean renal length was 113.5 +/- 6.1 mm on the right side and 114.6 +/- 6.6 mm on the left side. The mean increase in renal length after hydration was statistically significant (P < 0.001) and was 6.8% on the right side and 6.6% on the left side. Sex and age did not affect the measurements significantly.

Oral fluid intake causes a statistically significant increase in renal length. This observation should be taken into consideration when renal length measurements are clinicallly important.