In 2003, poison control centers took more than 90,000 calls from parents whose children had swallowed a foreign object. The vast majority of those objects were coins.

A child who turns himself into a human piggy bank can cause parents much concern, but unless there are signs of distress, physicians say it’s probably OK to wait it out.

Dr. Neil Ernst, a pediatrician with Cascade Medical Clinic in Redmond, says he sees a child who has swallowed a coin about once a year. But more often, those kids go straight to the emergency room.

”The size of the coin is really the key question,” he says. ”If it gets hung up, it usually has to be the size of a quarter or larger.”

Of course, that all depends on the size of the child as well. Ernst says the bigger concern is that the coin could block the windpipe or get stuck in the esophagus. If the child is choking, parents should conduct the Heimlich maneuver and call 911 immediately.

Any symptoms such as trouble handling saliva, coughing or retching, or trouble swallowing are indications the coin has gotten stuck and a trip to the emergency room is warranted.

At the hospital, physicians generally remove the coin with special equipment or procedures with the child under sedation. While that procedure is straightforward, it is not entirely without risks.

Recently, researchers at Children’s Hospital in Boston conducted a study with children who had a coin lodged in the esophagus but had none of the warning signs of distress. Half the children were sent to have to the coins removed as soon as possible, while others were put under observation and re-evaluated 16 hours after ingestion.

Recently, researchers at Children’s Hospital in Boston conducted a study with children who had a coin lodged in the esophagus but had none of the warning signs of distress. Half the children were sent to have the coins removed as soon as possible, while others were put under observation and reevaluated 16 hours after ingestion.

The doctors found that one in four of the children eventually passed the coin without any assistance. That same rate applied for the children who were pegged for immediate removal. By the time arrangements could be made to remove the coins, one in four of the children passed the coin on their own.

When coins did pass on their own, half passed within six hours, while the remainder passed within 16 hours. The researchers suggest that absent any symptoms, doctors should give the child between eight and 16 hours to pass the coin before subjecting them to anesthesia and a removal procedure.

If the coin is actually swallowed and makes its way into the stomach, chances are it will pass without worry.

”Coins are not hazardous beyond that point,” Ernst says, ”They generally end up in the Bend or Redmond sewer.”

The notable exception is post-1982 pennies. Researchers from Duke University Medical Center found that newer pennies can react with stomach acid to create a toxic mixture as corrosive as car battery acid.

In the late ’90s, a 2-year-old boy was brought to the center with an upset stomach. X-rays showed a small disc full of holes. The doctors assumed it was a toy part or a small battery. But when they removed the object, they found it was a 1989 penny the child had swallowed four days earlier. The child had developed a stomach ulcer in the area where the penny was lodged.

To discover what had happened, the physicians bathed pennies in a solution of stomach acid. Pennies minted before 1982, which are 95 percent copper and 5 percent zinc, showed no corrosion. However, newer pennies are nearly all zinc with a thin copper plating. Those began eroding immediately. Within two days, the post-1982 pennies had holes in them.

The physicians found the zinc in the coins reacted with the acid to form hydrogen gas and zinc chloride. The reaction is similar to the chemical process that occurs in car batteries, the physicians said. Other U.S coins are made of nickel and don’t have the same reaction. When a coin passes through the digestive system quickly, that’s usually not an issue. But if a penny gets stuck, it could be a concern.

If a child swallows a penny, the Duke physicians recommend waiting a day or two to see if the child will pass the coin. If the child experiences any stomach pain or vomiting, parents should take him or her to the emergency room right way.

Physicians also warn that small batteries, such as those typically used for watches or calculators, can leak and pose additional risk. If you know your child has swallowed a battery, contact your physician, poison control at 800-222-1222 or the National Button Battery Ingestion Hotline at 202- 625-3333.