The percentage of children in Pennsylvania with elevated blood lead levels is more than twice the national rate, according to new data published in JAMA Pediatrics.

Nationally, the number of children with elevated blood lead levels — at least five micrograms of lead per deciliter of blood — has declined precipitously, from 3% in 2016 to 1.9% in 2020. In Pennsylvania, 5% of children had elevated blood lead levels in 2020 — among the highest in the country, according to the study by Quest Diagnostics.

“We’re making progress, but it’s not fast enough,” said Harvey Kaufman, a senior medical director at Quest.

Lead in the blood can contribute to low IQ; speech, hearing, and behavior problems; and other developmental challenges. It can be especially dangerous in very young children.

Most sources of exposure are lead pipes in old water systems and lead paint, which is now banned but still present in old housing stock.

Blood lead levels among children gained national attention after the Flint water crisis, in which thousands of Michigan children were exposed to lead-contaminated water.

In Philadelphia, the tragic consequences of lead paint in rundown Philadelphia public schools and rental properties and in river ward neighborhoods with tainted soil were documented in The Inquirer’s prize-winning, two-year Toxic City series.

» READ MORE: Toxic City: The Ongoing Struggle To Protect Philadelphia’s Children From Environmental Harm

Reporters found that thousands of Philadelphia children had been poisoned by lead paint, in part because the city did little to protect families from rental properties with the now-banned substance, even after a child became ill.

Among numerous reforms spurred by The Inquirer’s reporting, Philadelphia stepped up enforcement of an existing law requiring landlords to certify their properties are lead-free before renting to families with young children and passed a new law requiring schools to certify they are “lead safe” annually.

Quest’s analysis of more than 1.1 million blood tests among children under age 6 between 2018 and 2020 from the laboratory company’s database reinforces data reported to the CDC that show a decline in elevated blood levels among children as states made progress in addressing lead pipes and lead paint.

But Kaufman and his colleagues estimated that at least half of children have detectable lead, which they defined as at least one microgram of lead per deciliter of blood.

The finding is troubling, Kaufman said, because it “tells you that it’s ubiquitous throughout the country.”

Pennsylvania was among the states with the highest portion of children with elevated blood lead levels. Only Nebraska (6%) and Ohio (5.2%) had a greater percentage of children with elevated blood lead levels.

Quest’s analysis included 77,445 Pennsylvania patients, with the largest volume of samples coming from the Philadelphia and Pittsburgh metro areas.