Canadian Task Force on Preventive Health Care

Structured Abstract

Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made.  (Formerly, these situations were captured under a "C Recommendation".)  This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade.  For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.

Screening Children for Lead Exposure in Canada
 

Adapted to the Canadian context by William Feldman, MD, FRCPC, Department of Pediatrics, University of Toronto, and Patricia Randel, MSc, former Task Force Research Associate (1992-94), from the report prepared for the U.S. Preventive Services Task Force by Carolyn DiGuiseppi, MD, MPH.

These recommendations were finalized by the Task Force in January 1994

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Objective

To make recommendations for universal screening to detect mild-to-moderate lead exposure in Canadian children.

Burden of Suffering

Short-term acute exposure to high levels of lead can cause a metallic taste, abdominal pain, vomiting, diarrhea, convulsions, coma or even death.  Long-term exposure may lead to anemia, learning disabilities and hyperactivity, problems with memory and attention span, as well as lack of appetite, abdominal pain, irritability and kidney function.  The prevalence of neurotoxic lead levels in asymptomatic children in Canada is unknown.  Surveys which have been conducted in Canada in the last fifteen years revealed that most Canadian children have blood lead levels below 10µg/dL and that the levels of lead exposure have declined.  Sources of lead in the environment include leaded paint, banned for household use due to an association with lead toxicity as measured by BPb levels; soil, lead levels near roadways and adjacent to lead smelters are typically thousands of times higher than natural levels; water, particularly when lead pipes are used for water supply; and air, which has declined as a result of the removal of lead from gasoline. Risk factors for elevated BPb levels relate either directly or indirectly to the sources of lead exposure described above.  The most important demographic risk factor is probably age.  Blood levels tend to rise after birth, peak between 18 months and 2 years of age, and decline gradually through adolescence.
 There is fair evidence that lead exposure as measured by tooth lead is associated with (perhaps not causally) a small reduction in IQ test scores.  However, significant, associations between concurrent BPb and visual-motor integration and delayed reaction times at low to moderate levels have been reported.  Lead exposure also effects red blood cells, typically causing anemia.

Options

Lead levels are ascertained using blood lead levels (capillary and venous sampling), Erythrocyte Protoporphyrin measurement, and questionnaires. Treatment options for children with severe lead exposure includes dimercaprol plus CaNa2-EDTA, EDTA, or succimer , and penicillamine. For children with mild-to-moderate lead exposure nutritional interventions included caloric, calcium or iron supplementation. Environmental deleading was also considered.

Outcomes

Adverse effects of lead exposure include anemia, a metallic taste, diarrhea, convulsion, coma, death, learning disabilities, hyperactivity, problems with memory and attention span, cognitive function, stature as well as lack of appetite, abdominal pain, irritability and impaired kidney function. Sensitivity and specificity were calculated for the laboratory tests. Prevention and treatment are designed to reduce the risk for adverse outcomes and reduce the rates of outcomes that are already present.

Evidence

These recommendations were adapted from materials prepared for the U.S. Preventive Services Task Force. MEDLINE was searched for 1989 to 1993 using the keywords lead or lead poisoning or plumbism with the subheading for potential lead sources such as dust and paint, screening methods, neurobehavioral testing and dysfunction in children, reproductive outcomes, environmental abatement and chelating agents. Study results were synthesized in table or graphic format only.

Recommendations were graded as:

A 
 Good evidence to support the recommendation that the condition be specifically considered in a PHE. 
B 
 Fair evidence to support the recommendation that the condition be specifically considered in a PHE. 
C 
 Poor evidence regarding inclusion or exclusion of the condition in a PHE, but recommendations may be made on other grounds. 
D 
 Fair evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE. 
E 
 Good evidence to support the recommendation that the condition be specifically excluded from consideration in a PHE. 
Quality of evidence was rated according to 5 levels:

I 
 Evidence from at least 1 properly randomized controlled trial (RCT). 
II-1 
 Evidence from well-designed controlled trials without randomization. 
II-2 
 Evidence from well-designed cohort or case-control analytic studies, preferably from more than 1 centre or research group. 
II-3 
 Evidence from comparisons between times or places with or without the intervention. Dramatic results in uncontrolled experiments could also be included here. 
III 
 Opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees. 

Values

The 13-member Task Force of experts in family medicine, geriatric medicine, pediatrics, psychiatry and epidemiology used an evidence-based method for evaluating the effectiveness of preventive health care interventions. Recommendations were not based on cost-effectiveness of options. Patient preferences were not discussed.

Background papers providing critical appraisal of the evidence and tentative recommendations prepared by the chapter author were pre-circulated to the members. Evidence for this topic was presented and deliberated upon in 1- to 2-day meetings from October 1993 to March 1994. Consensus was reached on final recommendations.

Benefits, Harms, and Costs

Blood lead concentrations do not necessarily represent lead toxicity. Although blood tests for lead have good precision and accuracy, they cannot differentiate between a recent exposure to a high level of lead or chronic exposure resulting in a steady state. Costs are also high and the test is slow and cumbersome. Erythrocyte Protoporphyrin measurement is inexpensive, unaffected by environmental lead contamination, is easily done on capillary blood specimens, and is a better indicator of chronic lead exposures. It lacks sensitivity and specificity in the low-to-moderate range using blood lead levels as the reference standard. Questionnaires have not been tested for detection of lead.

No controlled trials have been done to evaluate routine screening compared with targeted or case-finding, universal screening or health benefits of screening to detect mild-to-moderate exposure, or interventions for person with mild to moderate exposure to assess better.

Trials of targeted screening have not been done, but uncontrolled time series suggest that screening high-risk populations may be effective in improving clinical outcomes when compared with case-finding. Soil abatement measures do not reduce lead levels in children although residential deleading reduces lead levels in children with levels 25 g/dL. Treatment of children with high levels of lead with dimercaprol plus CaNa2-EDTA or succimer reduces their levels of lead to below the levels where the risk of enceopalopathy or death can occur. EDTA chelation therapy and penicillamine reduce moderate lead levels in the short term. No controlled trials of nutritional interventions have been done.

Adverse effects of drug therapy are present for all therapies although succimer and penicillamine have lower levels. Adverse effects of screening include venipuncture infections or bleeding (minimal) costs, inconvenience, and anxiety, although these have not been evaluated in controlled studies. EDTA chelation therapy is invasive, takes up to 8 hours per session, and has caused renal failure or death in high doses, and depletion of zinc stores.

Recommendations

Recommendation grade [A, B, C, D, E]  and level of evidence [I, II-1, II-2, II-3, III] are indicated after each recommendation. Citations in support of individual recommendations are identified in the guideline text.

Validation

This report was externally peer reviewed. The Royal Society of Canada recommends screening of children who live in areas of high lead levels plus screening during cleanup, and wherever possible screen for lead during other health testing. The U.S. Centers of Disease Control and Prevention recommend that universal screening of all children aged 6 months to 6 years except in communities where it has been shown that children are not exposed to lead, use a brief questionnaire to screen for children who are at high-risk for high-dose lead exposure starting at 6 months or at 12 to 15 months for all other children, and instruct pediatric health-care providers to teach parents how to prevent lead exposure, tailoring guidance to likely hazards in the community.

Sponsors

The Canadian Task Force on the Periodic Health Examination developed this guideline with funding from Health Canada.

Documents

Source

Link to Full Text of this review

Link to Summary Table of Recommendations of this review

Link to Selected References list of this review

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