A smartphone app can accurately detect early symptoms of biliary atresia (BA) - a rare disorder that accounts for nearly half of paediatric end-stage liver disease in the US.

According to a study, researchers from the Johns Hopkins Children's Centre reported they have verified the ability of the free app, called PoopMD, to accurately read, interpret and record the colour of a newborn's stool as a possible early symptom of BA.

Parents using the app can rely on it to help detect the symptomatic pale yellow to chalky grey stools that mean urgent medical assessment is needed. PoopMD is free and available for Apple and Android smartphone users.

"Days matter in diagnosing BA," said Douglas Mogul, lead author of the study published in Public Library of Science (PLOS) ONE journal. Babies with BA treated within the first two months of life have the best outcomes and are far less likely to need a liver transplant later.

For the study of the app, the team first gathered the medical opinions of seven paediatricians who looked at 34 photographs of pale-coloured stool.

Twenty-seven of the pictures were determined to be of normal stool, and seven were deemed bile deficient, signalling high risk for BA.

Next, one expert and three laypeople were asked to use the app on Apple and Android devices to look at and analyse the same pictures using a variety of smartphone models.

"These individuals were essentially asked to take a picture of the stool photograph and determine if the app identifies the photo as normal or pale," Mogul said.

Even with the picture of the picture, the researchers said, the app correctly identified all of the abnormal stool samples and correctly identified 24 of the 27 normal stools, while three normal stools were mislabelled "indeterminate".

"That means the app never identified a normal stool as pale, a type of false positive that could cause unnecessary anxiety for a parent or other app user," Mogul said.