HOW RELIABLE ARE ULTRASOUND MEASUREMENTS OF RENAL LENGTH IN ADULTS

Ultrasound assessment of patients with renal impairment commonly inclu des measurement of bipolar renal length. Reduction in length is consid ered to indicate chronic renal disease and is a factor in deciding whe ther to proceed to renal biopsy. To date, no published data are availa ble on interobserver and intraobserver variation in sonographic renal length measurement in adults. Bilateral renal lengths were measured in 20 adult subjects, with no history of renal disease, by three experie nced operators, on two separate occasions. Limits of agreement for rep licate measurements by each ultrasonographer and for replicate measure ments by each pair of ultrasonographers were determined. Values of rep eatability (a measure of intraobserver variation) and reproducibility (a measure of interobserver variation) were calculated for all renal l ength measurements, and for right and left renal lengths separately. R esults indicate that replicate renal length measurements differ by les s than 1.85 cm in 95% of cases, and the magnitude of variations is sim ilar when measurements are made by either single or different ultrason ographers, and are similar for right and left renal length measurement s. This suggests that sonographic bipolar renal length measurements in normal adult kidneys are reasonably reliable. In diseased kidneys, ho wever, in which identification of renal poles is difficult, interobser ver and intraobserver variation may be much greater.