Blood Lead Tests
Chronic lead exposure is a serious problem that can have severe effects on a child’s brain development. Kids can be exposed to lead through old paint, contaminated soil and even toys. It has a direct effect on IQ, and classroom behavior. In 1992, Congress passed the Residential Lead-Based Paint Hazard Reduction Act to require disclosure of lead paint in homes. In 2021, half of US children had detectable lead levels in their blood.
Currently, there are 48 states, plus Puerto Rico, and DC, with state-wide CDC-funded lead testing programs. Many states require blood lead tests before a child may enroll in preschool or grade school. Although there is no safe level of lead in children’s blood, the CDC has recently reduced the reference point from 10 micrograms to decileter to 5 and now to 3.5 micrograms per decileter.
There are two ways to do this test. The first, and simpler way, is using capillary blood. The child’s finger is pricked, blood is drawn into a thin tube or vial, and that blood is tested in the doctor’s office. The other way is to draw a venous sample from the child. The capillary blood tests are point of care tests cleared by the FDA under the 510k process. Since 1997, all five of the cleared products have been produced by the same company; of those five tests, four are moderate complexity and one is CLIA waived. CLIA waived tests are those that are essentially simple and can be done at home; moderate complexity or high complexity tests must be done in CLIA-certified laboratories. The only test with a CLIA waiver is the Lead Care II.
In 2019, the USPSTF reviewed available evidence and concluded that it is not clear that screening children for lead exposure is beneficial, however at that time it did find that the capillary testing was accurate. Nonethless, it “concluded that the current evidence is insufficient, and that the balance of benefits and harms of screening for elevated blood lead levels in asymptomatic children 5 years and younger and in pregnant women cannot be determined.” In particular, there is limited evidence that chelation therapy has any short or long term benefit.
On one hand, blood lead testing is incredibly important, and having point of care tests available for immediate results with only a small blood sample has demonstrably increased testing. On the other hand, there are numerous concerns with the utility and accuracy of these tests.
A large metanalysis of blood lead test studies showed that capillary testing was extremely accurate when the cutoff was 10 or 20 micrograms per decileter. When CDC lowered the reference to 5 micrograms per decileter, in 2013, some scientists expressed concern that the point of care tests could not be reliable at that level. They were, nonetheless, deployed widely.
The Lead Care II, as well as other blood lead tests, have been an issue of concern for years. FDA and CDC worked together to make the public aware of the potential for false results with these tests, as far back as 2014. In 2017 Magellan filed reports with the FDA about inaccurate results. The issue, at that time, was around the type of tube the blood was collected in, so was only relevant for venous blood draws (the test was mainly used with capillary samples). The company provided revised instructions to its customers to mitigate the false negatives. That did not appear to solve the problem. In 2017 and 2018, FDA issued public communications about the tests, and performed inspections and issued warning letters to the companies. In 2021, FDA issued three recalls for point of care blood tests.
The question remains if point of care lead testing, with the current technology, is useful. If more patients are getting false negatives, being falsely assured that their child’s intellectual and behavioral issues are not due to lead when they are, that is surely a disservice. However, studies have also not shown that chelation therapy, home lead abatement or nutritional interventions work to help reduce blood lead levels in children. So even a true positive may, in fact, not be all that clinically useful. As far as we can tell, capillary blood tests are not consistently reliable, even if they were, the margin of error is greater than the current reference point so results aren’t valid. And if interventions don’t help, then there does not appear to be a clear need for these tests. Yet, the test itself is relatively harmless. On balance, is it better to do a test that is relatively simple, likely inaccurate with limited efficacious treatment options? Despite what the USPSTF says, many states and school districts still require this test. Perhaps, with better testing and better interventions, the answer would be more clear.