Am Fam Physician. 2007;76(5):691-694
This statement summarizes the U.S. Preventive Services Task Force (USPSTF) recommendations on screening for elevated blood lead levels in children and pregnant women and the supporting scientific evidence, and it updates the 1996 recommendations contained in the Guide to Clinical Preventive Services, 2nd ed.1 Explanations of the ratings and of the strength of overall evidence are given in Table 1 and Table 2, respectively. The complete information on which this statement is based, including evidence tables and references, is included in the evidence update2 on this topic, available on the USPSTF Web site athttp://www.uspreventiveservicestaskforce.org. The recommendation is also posted on the Web site of the National Guideline Clearinghouse athttp://www.guideline.gov.
| The USPSTF grades its recommendations according to one of five classifications (A, B, C, D, or I) reflecting the strength of evidence and magnitude of net benefit (benefits minus harms). | |
| A. | The USPSTF strongly recommends that clinicians provide [the service] to eligible patients.The USPSTF found good evidence that [the service] improves important health outcomes and concludes that benefits substantially outweigh harms. |
| B. | The USPSTF recommends that clinicians provide [the service] to eligible patients.The USPSTF found at least fair evidence that [the service] improves important health outcomes and concludes that benefits outweigh harms. |
| C. | The USPSTF makes no recommendation for or against routine provision of [the service].The USPSTF found at least fair evidence that [the service] can improve health outcomes but concludes that the balance of benefits and harms is too close to justify a general recommendation. |
| D. | The USPSTF recommends against routinely providing [the service] to asymptomatic patients.The USPSTF found at least fair evidence that [the service] is ineffective or that harms outweigh benefits. |
| I. | The USPSTF concludes that the evidence is insufficient to recommend for or against routinely providing [the service].Evidence that [the service] is effective is lacking, of poor quality, or conflicting, and the balance of benefits and harms cannot be determined. |
| The USPSTF grades the quality of the overall evidence for a service on a three-point scale (good, fair, or poor). | |
| Good: | Evidence includes consistent results from well-designed, well-conducted studies in representative populations that directly assess effects on health outcomes. |
| Fair: | Evidence is sufficient to determine effects on health outcomes, but the strength of the evidence is limited by the number, quality, or consistency of the individual studies; generalizability to routine practice; or indirect nature of the evidence on health outcomes. |
| Poor: | Evidence is insufficient to assess the effects on health outcomes because of limited number or power of studies, important flaws in their design or conduct, gaps in the chain of evidence, or lack of information on important health outcomes. |
The USPSTF is redesigning its recommendation statement in response to feedback from primary care physicians. The USPSTF plans to release in 2007 a new, updated recommendation statement that is easier to read and incorporates advances in USPSTF methods. The recommendation statement below is an interim version that combines existing language and elements with a new format. Although the definitions of grades remain the same, other elements have been revised.
Summary of Recommendations
CHILDREN
The USPSTF concludes that evidence is insufficient to recommend for or against routine screening for elevated blood lead levels in asymptomatic children one to five years of age who are at increased risk. I recommendation.
The USPSTF recommends against routine screening for elevated blood lead levels in asymptomatic children one to five years of age who are at average risk. D recommendation.
PREGNANT WOMEN
The USPSTF recommends against routine screening for elevated blood lead levels in asymptomatic pregnant women.D recommendation.
Rationale
Importance. Blood lead levels in children have declined dramatically in the United States over the past two decades. However, segments of the population remain at increased risk for higher blood lead levels. Even relatively low blood lead levels are associated with neurotoxic effects in children. Severely elevated blood lead levels in symptomatic pregnant women are associated with poor health outcomes; however, lead levels in this range are rare in the U.S. population.
Detection. There is good evidence that venous sampling accurately detects elevated blood lead levels and fair evidence that validated questionnaires are modestly useful in identifying children at increased risk for elevated blood lead levels.
Benefits of Detection and Early Intervention. The USPSTF found good-quality evidence that interventions do not result in sustained decreases in blood lead levels and found insufficient evidence (no studies) evaluating residential lead hazard control efforts (i.e., dust or paint removal, soil abatement, counseling, or education) or nutritional interventions for improving neurodevelopmental outcomes in children with mild to moderately elevated blood lead levels. The USPSTF found no evidence examining the effectiveness of screening or interventions in improving health outcomes in asymptomatic pregnant women. Given the low prevalence of elevated blood lead levels in children at average risk and asymptomatic pregnant women, the magnitude of potential benefit cannot be greater than small.
A theoretical benefit of screening is that identification may prevent lead poisoning of other persons in a shared environment, but the magnitude of this theoretical benefit is uncertain.
Harms of Detection and Early Treatment. There is good-quality evidence that chelation treatment in asymptomatic children does not improve neurodevelopmental outcomes and is associated with a slight diminution in cognitive performance. Chelation therapy may result in transient renal, hepatic, and other toxicities; mild gastrointestinal symptoms; sensitivity reactions; and rare life-threatening reactions. Residential lead-based paint and dust hazard-control treatments may lead to acutely increased blood lead levels from improper removal techniques. Potential harms of screening are false-positive results, anxiety, inconvenience, work or school absenteeism, and financial costs associated with repeated testing. Although the exact magnitude of these known and potential harms is uncertain, the overall magnitude is at least small.
No studies have directly addressed the harms of screening and interventions for pregnant women. Although there is little specific evidence concerning the potential harms of interventions for pregnant women with elevated blood lead levels, the magnitude of harms from such interventions is also at least small.
USPSTF Assessment. The USPSTF concludes that the evidence is insufficient to assess the balance between potential benefits and harms of routine screening for elevated blood lead levels in children at increased risk. Given the significant potential harms of treatment and residential lead hazard abatement, and no evidence of treatment benefit, the USPSTF concluded that the harms of screening for elevated blood lead levels in children at average risk and in asymptomatic pregnant women outweigh the benefits.
Clinical Considerations
This USPSTF recommendation addresses screening for elevated blood lead levels in children one to five years of age who are at average or increased risk and in asymptomatic pregnant women.
The highest mean blood lead levels in the United States occur in children one to five years of age (geometric mean, 1.9 mcg per dL [0.10 μmol per L]). Children younger than five years are at greater risk for elevated blood lead levels and lead toxicity because of increased hand-to-mouth activity, increased lead absorption from the gastrointestinal tract, and the greater vulnerability of the developing central nervous system. Risk factors for increased blood lead levels in children and adults include minority race or ethnicity; urban residence; low income; low educational attainment; older housing (pre-1950); recent or ongoing home renovation or remodeling; pica exposure; use of ethnic remedies or certain cosmetics; exposure to lead-glazed pottery; occupational and para-occupational exposures; and recent immigration. Additional risk factors for pregnant women include alcohol use, smoking, pica, and recent immigration status.
Blood lead levels in childhood, after peaking at about two years of age, decrease during short- and long-term follow-up without intervention. Most lead is stored in bone. High bone lead levels can be present with normal blood lead levels, so blood lead levels often do not reflect the total amount of lead in the body. This could explain the lack of effect of blood lead level-lowering measures on reducing neurotoxic effects.
Screening tests for elevated blood lead levels include free erythrocyte (or zinc) protoporphyrin levels and capillary or venous blood lead levels. Erythrocyte (or zinc) protoporphyrin is insensitive to modest elevations in blood lead levels and lacks specificity. Measurement of blood lead concentration is more sensitive than erythrocyte protoporphyrin for detecting modest lead exposure, but its accuracy, precision, and reliability can be affected by environmental lead contamination. Therefore, venous blood lead level testing is preferred to capillary sampling.
Screening questionnaires may be of value in identifying children at risk for elevated blood lead levels but should be tailored for and validated in specific communities for clinical use.
Treatment options in use for elevated blood lead levels include residential lead hazard-control efforts (i.e., counseling and education, dust or paint removal, and soil abatement), chelation, and nutritional interventions. In most settings, education and counseling are offered for children with blood lead levels of 10 to 20 mcg per dL (0.50 to 0.95 μmol per L). Some experts have also recommended nutritional counseling for children with blood lead levels in this range. Residential lead hazard control is usually offered to children with blood lead levels of 20 mcg per dL or greater, whereas chelation therapy is offered to children with blood lead levels greater than 45 mcg per dL (2.15 μmol per L).
Community-based interventions for the primary prevention of lead exposure are likely to be more effective and may be more cost-effective than office-based screening, treatment, and counseling. Relocating children who do not yet have elevated blood lead levels but who live in settings with high lead exposure may be especially helpful. Community, regional, and national environmental lead hazard reduction efforts, such as reducing lead in industrial emissions, gasoline, and cans, have been proven highly effective in reducing population blood lead levels.
The Discussion section that usually is included in USPSTF recommendation statements is available in the full recommendation statement on the USPSTF Web site athttp://www.ahrq.gov/clinic/uspstf06/lead/leadrs.htm.
Recommendations of Others
The Centers for Disease Control and Prevention (CDC) recommends universal screening in communities where 12 percent or more of children one to three years of age have elevated blood lead levels; or in communities that do not have prevalence data, if 27 percent or more of the housing was built before 1950. The CDC recommends targeted screening for all other children based on an individual risk assessment, including whether children receive Medicaid; Supplemental Food Program for Women, Infants and Children; or other forms of governmental assistance.3 This approach is also supported by the American College of Preventive Medicine.4
The American Academy of Pediatrics (AAP) recommends that physicians learn whether city or state health departments provide guidance for screening children who are not eligible for Medicaid. If no such guidance is available, the AAP recommends that physicians consider screening all children. Ideally, children should be tested at one and two years of age.5
The American Academy of Family Physicians recommends screening infants 12 months of age for lead poisoning if they live in communities in which the prevalence of lead levels requiring intervention is high or undefined; if they live in or frequently visit a home built before 1950 that has dilapidated paint or recent or ongoing renovations or remodeling; if they have close contact with a person who has an elevated blood lead level; if they live near lead industry or heavy traffic; or if they live with someone whose job or hobby involves lead exposure, who uses lead-based pottery, or who takes traditional remedies that contain lead.6
Medicaid's Early and Periodic Screening, Diagnostic, and Treatment Program requires that all children receive a screening blood lead test at 12 and 24 months of age; children 36 to 72 months of age must receive a screening blood lead test if they have not been previously screened for lead poisoning.7,8
No national organizations currently recommend screening pregnant women for elevated lead levels.
editor's note: To further clarify the clinical considerations regarding screening tests for elevated blood lead levels, venous or capillary sampling is more sensitive than free erythrocyte (or zinc) protoporphyrin level testing. However, environmental lead contamination can affect the accuracy, precision, and reliability of capillary sampling, resulting in higher reported false-positive results than with venous sampling. Thus, venous blood level testing is preferred.