Connie Hill of Columbus, Ohio, got some unsettling news after her son's 12-month checkup.

A nurse called to say that the 1-year-old's blood lead level test had come back as slightly elevated, which would put him in the top 2.5 percent of lead-exposed children ages 1 to 5 in the United States.

That was alarming, because according to the Centers for Disease Control and Prevention, even low blood lead levels can have long-term effects on a child's IQ, academic achievement and ability to pay attention.

Luckily, the reading was a false alarm. The pediatrician had taken the blood sample using a tool known as a heel-stick test, which involves pricking the skin to collect blood. At the pediatrician's recommendation, Hill had her son's lead level reanalyzed using blood that was drawn from a vein. The results of this second test came back from the lab as "less than 3 micrograms of lead per deciliter of blood" — the lowest possible reading for that lab's particular testing equipment.

"I was obviously very relieved," says Hill. "But I was still a bit confused about [which test] was giving me the correct information."

Hill was also somewhat concerned that even the second test suggested that there could be some lead in her son's blood. "I know that any lead in their system isn't OK, really," she says.

The water contamination crisis in Flint, Mich., has driven increased attention to the need to test for lead exposure. But children can be exposed to lead from other sources, including paint, soil, toys and candy. More than half a million children ages 1 to 5 had high blood lead levels in 2010, according to the CDC.

But as Hill discovered, lead testing can be confusing. We spoke with scientists and doctors to find out what Hill and other parents should know about lead testing in children.

When should a child be tested for lead?

All children suspected of lead exposure should have their blood lead level analyzed. But state laws and medical associations differ on whether or how often children with no obvious risk factors or symptoms of lead poisoning should be tested.

The American Academy of Pediatrics recommends that doctors speak with parents about potential risk factors such as lead paint in the home during regular well visits, and then only test blood lead levels if there is reason to believe a child may be at risk.

But states often have their own guidelines for lead testing that may require pediatricians to test all infants and children at specific ages.

The bottom line, says Dr. Megan Sandel, a pediatrician at Boston Medical Center, is that any parents who are worried should request that their kids be tested even if there is no obvious risk of lead poisoning. "Having a parent concerned tips the balance," she says.

The less painful option isn't always the most accurate.

There are two main methods for collecting blood samples for lead screening. The first goes by the names capillary test, finger-stick and heel-stick. For this method, a medical professional pricks a child's finger or heel to collect a few drops of blood.

The second option is the venous blood draw, which requires that the medical professional use a needle to draw blood from a vein in the child's arm.

Many pediatricians prefer the capillary test. "A prick to the finger is quicker and easier," explains Sandel. She says that on babies especially, it can be challenging for doctors to find a vein to draw blood, and it can be difficult for parents to sit and watch their baby or child cry.

Additionally, the finger-stick is easier to offer outside of a doctor's office. "It can be done in the field, whereas the IV test cannot," explains neurotoxicologist Deborah Cory-Slechta of the University of Rochester Medical Center. That means health professionals can test children in schools and homes, reaching children who may not make regular doctor visits.

As Hill and other parents have learned, the downside of the finger-stick is that it can result in a false positive.

"If there is any dust from lead on your fingertips, [the finger-stick] will pick up that dust and attribute that to your blood," says Sandel. "The pro of the vein test is that it's much more accurate because it's actually measuring the level of lead in the blood."

For this reason, when a capillary test results in a high lead level reading, doctors order a venous test to confirm whether the blood lead level is actually high.

Laboratory analysis vs. in-office results.

A key distinction between the many different blood lead testing instruments is how quickly they generate results.

Many doctors send samples to a laboratory for analysis. Parents then hear from their pediatrician's office when the results are ready, which often takes about a week.

A more rapid method, the LeadCare II Blood Lead Test System, that can analyze both venous and finger-stick blood samples, returns results in minutes and can be used in the doctor's office while the patient waits.

Sometimes doctors have difficulty reaching parents to tell them that a lead test came back high, says Courtney Lias, director of the Division of Chemistry and Toxicology Devices at the Food and Drug Administration. "That access is a real benefit [of this test]," says Lias. "It allows more people to be tested for lead."

If the test result is high, a doctor can immediately notify parents and discuss steps to remove lead from a child's environment.

How low is low enough?

Sandel and Cory-Slechta were both on the 2012 CDC Advisory Committee on Childhood Lead Poisoning Prevention that determined that no level of lead, however low, is safe in children.

Prior to 2012, the CDC considered blood lead levels of 10 micrograms per deciliter or higher the trigger for follow-up screening and discussions of how to remove lead from a child's environment. After the report, the level that should trigger action dropped to 5 micrograms per deciliter or greater.

For children with blood lead level readings below 5, interpreting the results is a bit complicated.

A low reading may mean that there is actually no lead in a child's system at all. "Even the blood testing by the vein is only accurate within 1 or 2 points," explains Sandel. "So a blood lead level of 2 means that there isn't any lead, or that it is a point or 2 higher."

Also, while Sandel, Cory-Slechta and public health advocates say that we as a society could be doing much more to protect children from risk factors like lead paint in older homes, parents may not be able to completely eliminate lead from a child's environment.

"The reality is that we are somewhat paying the price of industrialization and the fact that the average lead level for kids in the 1970s was 15," Sandel says. "What has essentially happened is that background exposure from many years ago is still around. Your ability as a parent to totally avoid that lead is really limited."

The most important things parents can do, Sandel says, is to take whatever measures they can to remove lead from their homes and to make sure that when their children are tested, they actually see the results.

"The assumption is often no news is good news," says Sandel. She sometimes has parents say that no one called with the results. Even if a blood lead level test comes back low, parents should make sure they see the exact reading. "It's an important result to know that it was definitively OK."

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