Without testing, more children will be unknowingly exposed to high levels of lead, which can cause permanent damage to the brain, heart and kidneys.

Childhood testing for lead poisoning fell steeply at the beginning of the pandemic, as many families deferred routine medical care and clinics sought to limit in-person visits.

More than two years later, lead testing in many states has yet to rebound to prepandemic levels, leaving thousands of children at risk of irreversible damage to their health, according to state data obtained by NBC News.

Of 15 states that released recent numbers, all but one reported fewer childhood lead tests performed last year, as compared to 2019 — with more than 178,000 fewer children tested in total.

One of the sharpest declines was in Michigan, which saw testing fall by nearly a third since 2019, according to preliminary data from the state health department. That means that nearly 47,000 fewer children younger than 6 were tested last year in a state with a history of high lead exposure.

Many cases of lead exposure may be going undetected as a result, medical experts say, as there are often few visible symptoms of poisoning. That means more children will be unknowingly exposed to high levels of lead, which can cause permanent damage to the brain, heart and kidneys, as well as lifelong cognitive and behavioral problems. And children whose lead poisoning goes undetected are also missing the opportunity for early intervention that can reduce some of the harmful effects through dietary changes and developmental therapy.

“There is no safe level of lead, but children with lead exposure often don’t look sick,” said Dr. Jennifer McDonald, a consulting physician for the Michigan health department. “If we know, we can intervene. If we don’t have a test, we don’t know.”

Public health experts are also concerned about the extended time children have spent in lead-contaminated homes during the pandemic, as exposure most frequently happens through breathing in dust from lead paint, ingesting paint chips, playing in contaminated soil or drinking water contaminated by lead pipes. The pandemic has slowed in-home lead removal efforts that are often prompted by a test showing elevated levels of the toxin.

Many states with significant drops in testing — including Colorado, Washington and South Carolina — attributed the decline to the ongoing impact of the pandemic, as many families have remained reluctant to bring their children in for routine checkups. Some states also tied low testing numbers to a national recall of lead test kits last year.

“It can’t be overstated how much the coronavirus pandemic kept parents and children out of clinics for regular and follow-up visits,” said David Morgan, a health department spokesman for New Mexico, which saw a 30 percent decline in lead testing last year, as compared to 2019.

Nationally, lead exposure tends to be highest among Black children and those living in areas of high poverty. Children younger than 6 are the most vulnerable, as their bodies are rapidly developing, and they are more likely to put lead-contaminated objects in their mouths. Young children are also unable to get vaccinated against Covid.

Dr. Lynn Smitherman, a pediatrician in Detroit, said that well-child visits at her practice were starting to pick up last year when the Covid omicron variant hit, and appointments suddenly dropped by 50 percent.

“We were open, but families were afraid,” said Smitherman, whose practice largely serves children from low-income families. In recent weeks, routine visits have begun increasing again, but the practice is still playing catch-up, she said. “We are not where we should be — we are still backtracking and getting patients who should have been screened last year.”

The pandemic also prompted some lead-testing sites in Michigan to close or reduce their hours because of limited staffing.

Children in Michigan are at significant risk of lead poisoning, not only from lead pipes — which contributed to the water crisis in Flint — but also from its older housing stock. Much of the state’s housing was built before 1978, when the federal government banned the use of lead-based house paint. In Detroit, about 6.7 percent of children tested in 2019 had elevated lead levels, according to state data — more than three times the national average.

TaNiccia Henry, a Detroit resident, remains anxious about Covid and says family members have avoided basic medical care because of the virus. She would have been reluctant to bring her 2-year-old grandson to the doctor’s office last year had it not been for his older brother, who was found to have acute lead poisoning when he was 4.

“A lot of people just don’t know how serious elevated blood levels could be — I didn’t know, I had no clue. But it’s a must,” said Henry, who is now an activist for lead poisoning prevention. Her older grandson still has difficulties with handwriting, memory and attention from the lead poisoning, which she suspects may have come from lead-based paint and tile in their 100-year-old home.

She has since repainted the house, and the family no longer drinks tap water, for fear of contaminated lead lines. Both her grandsons still have lead detected in their blood, but they remain below elevated levels.

The most acute cases of lead poisoning tend to involve toddlers who have eaten contaminated paint chips, which have a very sweet taste, said Dr. Kanta Bhambhani, director of the lead clinic at the Children’s Hospital of Michigan. Even those cases are usually only detected through routine testing, as common symptoms like behavioral changes tend to be very subtle, she said. “By the time we see symptoms, it might be very, very late.”

But the long-term damage can be tremendous. “The main problem is cognitive deficits that might not become evident until second, third, or fourth grade,” said Bhambhani, pointing to research linking lead exposure to higher school dropout and juvenile delinquency rates.

In some parts of Michigan, lead testing is frequently not done in doctor’s offices, instead requiring a trip to a hospital, health clinic or other facility. That creates additional barriers, especially for at-risk families who may struggle to find transportation and get time off work, said Dr. Mona Hanna-Attisha, a Michigan pediatrician who helped expose the Flint lead crisis when she noticed a spike in patients with elevated lead levels and suspected it was connected to contaminated drinking water.

“Even before Covid, it was really hard for people to come and see the doctor — we had a 20 to 30 percent no-show rate,” said Hanna-Attisha, who is the vice-chair of the statewide lead commission. “The pandemic exacerbated all of that.”

The Centers for Disease Control and Prevention estimated that more than 9,600 children with elevated blood lead levels across the country had missed being tested from January to May 2020. The agency does not yet have full data from state health departments for 2021, but said partial data from 29 states and Washington, D.C., indicated a 2 percent decline in the number of children tested from January through September of last year, as compared to the same period in 2019.

Childhood vaccination rates for measles, whooping cough and other infectious diseases have also fallen during the pandemic.

Some states point to other worrying signs. In Rhode Island, health officials found more children with elevated lead levels in both 2020 and 2021 than in 2019, even as testing has declined.

“This data suggests there may be a relationship between children spending a prolonged period in unhealthy housing environments and an increased risk of lead exposure and poisoning,” said Joseph Wendelken, a spokesperson for the state health department.

New Jersey saw a similar increase in children with elevated blood levels in 2020, despite the drop in testing, as well as a rise in hospitalizations for severe lead poisoning.

Lead exposure in the U.S. has fallen dramatically since the 1970s, when the issue became a major public health concern. Many states require lead testing, which is also mandatory for children enrolled in Medicaid. But even before the pandemic, only a fraction of U.S. children were routinely screened.

Alarmed by the drop-off in testing, state and local governments are making a new push to get children screened and to reduce exposure while the pandemic drags on.

In Michigan, officials have reached out to pediatricians, launched a media campaign targeting parents, and sponsored mobile testing events. Last month, the state also decided to expand medical support and lead removal services to children with lower levels of lead in their blood, following a recent change in CDC recommendations.

After reassigning lead-poisoning case managers and community advocates to focus on Covid when the pandemic began, Detroit started bringing workers back to its lead program last summer, said Denise Fair Razo, the city’s chief public health officer. The city has also expanded partnerships with day care centers and schools to test more children and catch those who may have missed their screenings.

She said local testing numbers are finally rising, but the city is still working to close the gap. “It’s a slow ramp-up,” she said. “We’re trying to get as many children tested as possible.”