Children with hearing loss who get ear tube surgery to address chronic ear infections may need tests before and after the procedure to see if their hearing improves, a U.S. study suggests.

When kids get an infection, fluid can build up in the middle ear, making it difficult for them to hear and potentially impairing speech and language development, said lead study author Dr. Kenneth R. Whittemore Jr., a researcher at Boston Children's Hospital.

"Completion of a hearing test after ear tubes are placed is important for a child who had hearing loss before the tubes," Whittemore said by email. "While the majority of the hearing losses resolve, there will be some patients who have previously unknown permanent hearing loss that will be present even after the placement of ear tubes."

Ear tube surgery is the most common operation performed on children, and roughly 667,000 kids in the U.S. alone get this procedure every year, Whittemore and colleagues note in JAMA Otolaryngology - Head and Neck Surgery.

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For the current study, researchers examined data on 2,274 patients who received ear tubes in 2010 and 2011. On average, patients were about 2.6 years old, although people up to age 24 were included.

Roughly 77 percent of kids had hearing tests before the surgery. About two-thirds had tests both before and afterward. Roughly 8 percent didn't get any hearing evaluations at all.

After surgery, about 20 percent of the patients who had preoperative evaluations had hearing loss.

In no case, however, did anyone with a normal preoperative hearing test have postoperative hearing loss, the authors reported

Within one year of surgery, 271 patients, or about 12 percent, had evidence of nonfunctional ear tubes, the study found.

Roughly 4 percent of the kids turned out to have hearing loss that might have been missed without tests after surgery, the study also found. That's because they had some hearing loss unrelated to ear infections.

One limitation of the study is that the exact type of hearing tests and the timing of these exams varied, the authors note.

Still, the findings suggest that postoperative hearing tests make sense for children who had problems before surgery, the authors conclude. Kids who didn't have hearing issues prior to surgery, however, might not need hearing tests afterwards.

Since 2013, the American Academy of Otolaryngology-Head and Neck Surgery has recommended hearing tests before kids get ear tubes, as well as follow-up exams afterward for those with some hearing loss in the first exam, the authors note.

The most common reason for persistent hearing loss after surgery is malfunctioning ear tubes, which can happen if the tubes come out prematurely or if wax or mucus or some other substances clogs them and makes them ineffective at helping fluid drain from the ear.

Less commonly, though, hearing loss can occur because of an underlying permanent problem unrelated to the tubes or fluid buildup from middle ear infections. Other problems include issues with the inner ear or nerve deafness, impaired ability of the ear to conduct sound or structural problems with the eardrum or bones in the middle ear.

"The take home message for parents is to make sure your doctor checks your child's hearing before surgery, and, if a hearing loss is found, to have the hearing checked again after tube placement to be sure it becomes normal," said Dr. Richard Rosenfeld, chairman of otolaryngology at SUNY Downstate Medical Center in Brooklyn, New York.

"Parents, and doctors, should not assume that the hearing loss is caused by the middle ear fluid," Rosenfeld, who wasn't involved in the study, added by email.