A new study shows that ultrasound is not enough to monitor kidney health in children with spina bifida. (Stock photo)
For decades, doctors have relied heavily on ultrasound scans to monitor kidney health in children with spina bifida, the most common permanently disabling birth defect in the U.S. People with spina bifida tend to develop end-stage renal disease up to 20 years earlier than the general population, so keeping a close watch on kidney health from a young age is important, says Children’s of Alabama pediatric urologist Stacy Tanaka, M.D. “Then if there’s a concern, it can be acted upon early and not ignored.”
Current guidelines from the Spina Bifida Association (SBA) recommend annual screening with ultrasound to look for hydronephrosis—a condition in which the urine backs up into one or more kidneys—as a sign of kidney function, and blood tests like serum creatinine, to measure overall kidney health. But with kids, Tanaka says, “the practice pattern was that a lot of people were only doing renal ultrasound.”
Now a new study from Tanaka and her Children’s colleague David Joseph, M.D., as well as other kidney experts from around the country, shows that ultrasound alone is not enough to assess kidney health. “We basically use ultrasonography as a reflection of renal function,” Joseph said, but few, if any, studies assessed its accuracy in determining renal function.
The study’s genesis came during a multidisciplinary meeting in 2003 of specialists who treat children with spina bifida. “The bottom line from all disciplines at that time was that nobody was really treating this population with evidence-based care,” Joseph said.
To change that, the Centers for Disease Control and Prevention and the SBA established the National Spinal Bifida Patient Registry (NSBPR), to which 20 spina bifida clinics submit data to help develop evidence-based care. In addition, nine clinics established a urologic protocol to manage and preserve initial renal function in young children with spina bifida (UMPIRE). The NSBPR and UMPIRE provided the data set Joseph and Tanaka used to determine the effectiveness of renal ultrasound vs. blood test to assess renal function.
The two registries included data on 2,500 children ages 1-18 with myelomeningocele, the most severe form of spina bifida. All had had an ultrasound and blood test within six months to determine estimated glomerular filtration rate (eGFR), a marker of kidney health.
The results were striking: ultrasound-based detection of hydronephrosis had only about a 25% sensitivity for identifying children with signs of chronic kidney disease in the UMPIRE study and 24% in the NSBPR cohort. That means kidney damage in three out of four children was going undetected. The poor sensitivity held even when researchers looked only at severe hydronephrosis, which had an even worse sensitivity rate–just 6% to 11%. “The renal ultrasound by itself wasn’t all that good,” Joseph said, “but that didn’t surprise us.”
The findings challenge current practice and suggest that blood tests measuring kidney function should be routinely performed alongside ultrasound, not just when ultrasound results look concerning, as some clinicians practice. The team at Children’s prefers testing for cystatin C rather than creatinine because of the test’s improved and more accurate ability to obtain an eGFR.
One reason clinicians may eschew blood tests is that it involves needles, Tanaka said, which be traumatizing for children. Ultrasound, on the other hand, is noninvasive, easily available, and can be performed by technicians.
“The ultrasound is very helpful and important,” Joseph said, “but you need to recognize that it may not be telling you about renal function or injury to the kidney.” The findings have already changed practice at Children’s, where all kids with spina bifida now receive both tests during kidney health screening.
Ideally, the next study would randomize kids to either double testing or ultrasound alone, but that requires significant funding, particularly since the children would need to be followed for years.
This study was conducted with very little financial support, Tanaka said. “It represents a labor of love for everyone at all nine UMPRIE centers who have been involved in this project,” Joseph added.
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