Urine tests unreliable for pediatric cholestasis screening: Study
Negative result doesn’t rule out disease, researchers say
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Testing for bilirubin, a liver damage marker, in urine is not reliable for screening or diagnosing cholestasis (slowed flow of the digestive fluid bile) in children, a study showed.
While a positive test result should prompt blood testing for bilirubin, a negative one does not rule out cholestasis, the researchers said.
“These findings indicate that urine bilirubin is not a suitable screening test for cholestasis,” they wrote.
The study, “Diagnostic Accuracy of Urine Bilirubin for Paediatric Cholestasis: Lessons From a Big Data Analysis,” was published as a brief report in Acta Pediatrica.
Cholestasis is when the flow of bile, a digestive fluid produced by the liver, slows or stops. It is a feature of several liver diseases, including biliary atresia, in which the tubes that carry bile are blocked or missing, preventing bile from reaching the intestines to aid digestion.
Data lacking on test’s accuracy for kids
When bile builds up in the liver, it can damage the organ and affect its ability to process bilirubin, a yellowish waste product normally converted in the liver to a form called direct bilirubin, which is eliminated from the body in bile. Liver damage can cause bile and both forms of bilirubin to leak into the bloodstream and be excreted in urine.
“In adults, a positive urine bilirubin [test] has shown 70%–77% sensitivity and 80%–82% specificity for identifying raised [blood] direct bilirubin,” the researchers wrote. “However, data in pediatrics are lacking.”
A test’s sensitivity is a measure of how well it can correctly identify a feature or condition in people who truly have it (true positives), while specificity is a measure of how well the test can correctly rule out people without that feature or condition (true negatives).
The team retrospectively reviewed medical records from a large Israeli database. They identified 75,964 pediatric patients who had both a urine test for bilirubin and a blood test for direct bilirubin within one week of each other. In total, 116,725 urine tests were done, usually on the same day as the blood test.
Participants had a mean age of 9.3, and 51% were boys. Only a small percentage (1.9%) were diagnosed with a liver disease. Those with a positive urine test had significantly higher blood levels of direct bilirubin and liver enzymes, another liver damage marker, than those without high bilirubin in urine.
Further statistical analyses showed that the urine test had low sensitivity (31.4%) but very high specificity (99.7%) for detecting high direct bilirubin in blood. Performance was also similar among the 11,775 children younger than 1, with a sensitivity of 27.1% and a specificity of 98.4%.
This means that if the urine test is positive, further blood testing for direct bilirubin is needed to confirm cholestasis. However, a negative urine test does not rule out cholestasis.
For example, most (79%) of the 34 children diagnosed with biliary atresia had a negative urine test at the time they first showed symptoms of cholestasis, “underscoring the limited utility of urine bilirubin for [biliary atresia],” the researchers wrote.
“Urine bilirubin should not be considered a reliable diagnostic or screening test in paediatric patients,” they added.
They emphasized that the study was limited by its retrospective nature and by the fact that most pediatric patients were not newborns, when blood sampling is difficult and urine testing could be helpful.
“The results may not be generalizable to [newborns],” the scientists concluded.
