Diagnostic criteria for assessing obstruction in the newborn with unilateral hydronephrosis using the renal growth-renal function chart.

Previous studies in newborns with unilateral hydronephrosis demonstrated that the contralateral normal kidney can rapidly compensate for changes in function in the hydronephrotic kidney by increasing or decreasing its growth rate. To formulate diagnostic criteria for assessing obstruction using compensatory growth responses we developed a renal growth-renal function chart that graphically describes the normal renal growth rate in young children. This chart allows changes in function in the hydronephrotic kidney to be graphically compared to changes in length of the contralateral normal kidney. The renal growth-renal function chart was used to assess obstruction in 47 neonates with primary unilateral hydronephrosis. Four reproducible, clinically relevant diagnostic patterns of differential function and growth were identified: 1) obstruction, 2) corrected obstruction, 3) no obstruction with good differential function (greater than 40%) and 4) no obstruction but poor differential function (less than 40%). The renal growth-renal function chart helped to identify and exclude obstruction, and provided welcome reassurance that nonobstructive hydronephrosis was not harming the kidney. It appears to have potential for improving diagnostic accuracy in newborns with hydronephrosis.