The findings suggest that some doctors may be unfairly suspicious of minorities and are overlooking actual abuse among whites, the researchers said.
"This study is a reminder to be as thorough and objective as possible in evaluating children with injuries," said Dr. Cindy Christian, who led the study at Children's Hospital of Philadelphia.
The researchers said the findings bolster suspicions that abuse among white children is underdiagnosed. They said it also points to another area of medicine where racial disparities and possible bias may affect health care.
They did not determine the race of the doctors involved, but they said they suspect that many were white and that the doctors' biases probably played a role in the findings.
"All of us have personal biases," Christian said. "It's human nature not to be able to see something negative in a person or group of people who are like you."
The findings were published in Wednesday's Journal of the American Medical Association.
The study involved 388 children under 3 who were treated for skull, arm or leg fractures at the Philadelphia hospital between 1994 and 2000. Two child-abuse experts reviewed the injuries and determined which ones were accidental and which were caused by abuse.
Minority children 1 year old and up with accidental injuries were over three times more likely to be reported to authorities for suspected abuse. They were also more likely to be subjected to a detailed type of X-ray often ordered when abuse is suspected.
Whether child abuse is more common among black and Hispanic children than among whites is uncertain; studies have had conflicting results. Most have concluded that low income is more strongly linked to abuse than race.
In the study, abuse was about twice as common among minority children. But racial differences in how children were evaluated remained even when the different rates were taken into account.
The study echoes research into shaken-baby syndrome that suggested abuse was commonly missed in children from white, well-educated parents "because those are the kinds of families that medical providers tend to suspect least," said Dr. Lawrence Ricci, a Maine pediatrician who specializes in child-abuse issues.
"Medical providers are taught, and need to be taught, to completely discount their impression of parents" and to focus on the child's injury, Ricci said.