Just one day after New Jersey became the first state to legislate and implement statewide pulse oximetry testing for critical congenital heart defects, doctors detected a heart murmur in newborn Dylan Gordon.

Dylan was the first of 19 infants in the state between Aug. 31, 2011, and April 30, 2015, to have a previously unsuspected heart defect found due to the non-invasive and inexpensive test that measures blood oxygen levels. The screening also enabled doctors to identify another 15 newborns with less severe congenital heart defects and nine other babies with other significant medical conditions that were previously unknown.

New Jersey was the first state to require screening of newborns since federal regulators recommended the measure in 2011. By December 2014, 43 states required screenings, according to the Centers for Disease Control and Prevention. (Connecticut, which does require screening for critical congenital heart disease, does not specifically require the pulse oximetry test.) Colorado, Washington, D.C., and Hawaii passed legislation requiring screenings in 2015.

The CDC report shows the states that have not enacted legislation or guidelines are Idaho, Wyoming, Kansas, Vermont and Florida.

Congenital heart defects are the most common birth defects in infants, affecting about 1 percent of babies. Most are mild, but about a quarter of those are critical congenital heart defects, or CCHDs, that require surgery or a medical procedure in the first year of life. In many cases, symptoms don’t show up in a normal physical exam, but a pulse oximetry test can indicate a problem.

Pulse oximetry measures blood oxygen levels and can detect seven critical congenital heart defects that could go unnoticed and lead to a child’s death within the first year if untreated, said Alex Kemper, M.D., Ph.D., a professor of pediatrics at Duke University and a member of the American Academy of Pediatrics.

The screening doesn’t catch all congenital heart defects, because not all are associated with low-oxygen levels, “but it does a pretty good job,” Kemper said. “Even those babies who turn out to have low oxygen levels for other reasons, you’re glad you had the screening.”

Kemper said pulse oximetry can also help pick up other conditions that might be difficult to identify otherwise, including sepsis or pneumonia.

Even as a growing number of states require pulse oximetry screening, the data collected from those results varies widely, according to the CDC report.

While a few states collect key details about each screening, including what the oxygen saturation was and how long after birth the test was done, others simply create aggregate numbers reflecting the total percentage of cases that failed. No other details are provided. Other states do not provide any data about how many have failed the screening.

Acknowledging barriers to data collection, such as lack of funding and technology, the report urged states to consider ways to improve their programs. One such way is the collection of individual-level data reporting.

“Collecting data related to factors associated with false-positive and false-negative results could help refine the recommended CCHD screening algorithm and screening activities,” the report said.

While all types of screening data can be valuable, “the most specific individual level results are the most important for surveillance, monitoring of outcomes and evaluation of the overall screening program,” said Jill Glidewell, a health scientist with CDC’s National Center on Birth Defects and Developmental Disabilities and the study’s lead author.

Gathering data on pulse oximetry findings has proven challenging for states that have passed such legislation. Other newborn screening is done using a heel stick blood test, which is analyzed at a central lab, with results entered into a comprehensive statewide database. By contrast, pulse oximetry readings are taken bedside and submitted later.

Health officials in Minnesota are working to eliminate potential data entry errors by having it collected electronically, an initiative that has proved expensive and difficult to implement throughout the state, said Amy Gaviglio, a genetic counselor who oversees newborn screening for the Minnesota Department of Health.

“For many states, this was an unfunded mandate and that has made it difficult to implement the way we know we should or collect data in the way we know we need to,” Gaviglio said. “The data collection is difficult, but I’m 1,000 percent convinced it’s the most important thing we’re doing for this screening.”

There are also complexities over where and how the screening is interpreted.

The calculations used to determine if a newborn passes or fails, or requires rescreening or additional testing leave room for interpretation, said Gaviglio, who is also co-chair of the CCHD Technical Assistance Work Group for the federal Health Resources and Services Administration and NewSTEPs, which facilitates information sharing among state programs. Altitude can also play a role in blood oxygen levels, requiring additional adjustments.

Performing the screening on babies in the neonatal intensive care unit is also difficult, both due to the tiny size of the infants and because many of the babies are already on supplemental oxygen that could throw off results.

The benefits of screening may vary based on location and on the prenatal care the mother has received. In rural areas, technology that could detect congenital defects early may not be available, making pulse oximetry screening crucial.

“Even though we may not have all the numbers we want, the anecdotal stories you hear from parents where this screening worked really make you keep moving,” Gaviglio said.