Evaluation of the patient presenting with suspected lead toxicity
History. Lead toxicity can be difficult to identify by the history and physical examination alone. Nonspecific symptoms in children are a clue: irritability, behavioral changes, changes in activity levels, developmental delay, and language delay.8 An expert panel formed by the Advisory Committee on Childhood Lead Poisoning Prevention of the CDC reviewed evidence of the effects of lead on academic performance and made recommendations to persons working with children. Deficits in IQ have been seen with blood levels as low as 5 mcg/dL. Attention deficits manifest as distractibility and impulsivity in children. Elevated blood levels of lead increase the likelihood of a diagnosis of attention-deficit/hyperactivity disorder (ADHD). Lead affects dopamine in the brain, leading to deficits in strategic planning and control of impulses. Deficits in visual–spatial skills have been associated with early lead exposure. Parents of children with lead poisoning typically report the development of behaviors such as restlessness, impulsivity, and/or aggression. Speech and language deficits have been studied extensively in relation to lead exposure in children. Children with lead toxicity may have difficulties with coordination, balance, and other fine and gross motor skills.10
Like the effects of other environmental toxins, the effects of lead in individual children will vary, so that screening questions aimed at determining the presence of risk factors are especially important. Even if no neurodevelopmental problems are apparent at the time a high blood level of lead is detected, the child is still at risk for future delays.10 Adults may have similar symptoms in addition to weak extensor muscles, delirium, or hallucinations.8
When eliciting a patient’s history, the primary care provider should ask questions about any past developmental delays, behavior problems, pica, or known exposures to lead. The provider should also ask about all places of residence, past and present; information on the age and condition of the homes (ie, chipping paint) and any current or previous renovations should be collected. Adults should be asked about hobbies and occupations, as these can result in exposure. The ingestion of “moonshine” also can affect blood lead levels.8
Physical examination. Typically, children with elevated blood levels of lead are asymptomatic, unless the levels are especially high.4 A mental status examination is an important element; however, it is most likely that only severe lead toxicity will result in notable changes. For example, a decrease in IQ or attention span would be difficult to detect during a physical examination and is more likely to be deduced from information in the history. Lead toxicity frequently is accompanied by iron deficiency, so the patient may have pale skin or exhibit lethargy.8,9 In adults with occupational lead toxicity, foot drop or wrist drop with decreased reflexes is common. This is because lead tends to affect the peripheral nervous system in adults, whereas in children the central nervous system is more likely to be affected. Every organ system is susceptible to the effects of lead.8 Adults may have lead lines in gingival tissue and may also have sleep disorders.8 Although the neurologic effects are more often considered, lead can also cause hypertension, renal injury, immunotoxicity, and reproductive problems.6 The characteristics of lead toxicity typical in children and in adults are summarized in Table 2.
Screening and laboratory tests. Although the CDC recommends screening questionnaires, the questionnaires currently used to identify exposure to lead have not been shown to be valid in recent studies. The sensitivity of the pediatric lead screening questions recommended by the CDC and American Academy of Pediatrics is low, even when the previous lead level guideline of 10 mcg/dL is used.13 The most recent guidelines reported by the US Preventive Services Task Force (USPSTF) are from 2006 and indicate that the specificity of the CDC questionnaires ranges from 32% to 75%.14 In a systematic review of lead screening questionnaires, including those from the CDC as well as state-specific modified questionnaires, the sensitivity and specificity demonstrated a wide range of values, and the questionnaires were not shown to be effective in determining risk for lead poisoning in children.15 Clearly, more research and modification of the existing screening questions are required in order to achieve the goal of preventing lead exposure. The sensitivity of techniques using geographic information system analysis is higher, and these can supplement questionnaires and aid in identifying persons living in high-risk areas.13 The CDC recognizes the geographic variability in lead exposure and therefore recommends that local and/or state agencies formulate recommendations based on local data. Furthermore, the CDC recommends blood lead level testing for any community with a percentage of pre-1950 houses of 27% or higher or a prevalence of blood lead levels of 10 mcg/dL or higher in children 12 to 36 months of age.5
Early identification through screening is especially important because patients with elevated lead levels are often asymptomatic.4 A whole-blood lead level is the standard diagnostic test and provides an approximation of lead in the body.8,16 Capillary finger-stick methods are appropriate for lead screening. However, because of the possibility of false-positive results with capillary samples, a venous blood draw is needed to confirm a positive result.5,16 A blood lead level higher than 70 mcg/dL is deemed an emergency because of the risk for encephalopathy.8 The American Academy of Pediatrics recommends that children undergo risk assessments for lead exposure at the ages of 6, 9, 12, 18, and 24 months and the ages of 3, 4, 5, and 6 years (Figure 3). Blood lead levels may be measured if the risk assessment is positive. However, many state Medicaid programs require blood lead level tests at the ages of 12 and 24 months because of the higher prevalence of lead toxicity in lower socioeconomic classes. Children who are recent immigrants, refugees, or adoptees are also at increased risk and should be screened no matter what their age. Although blood lead levels can be used to identify acute toxicity, a relatively low level does not necessarily rule out lead poisoning earlier in life.16 The American Academy of Pediatrics recommends that for children with blood lead levels of 5 mcg/dL or higher before the age of 6 years, levels should be measured again at the ages of 3, 4, and 5 years. Any child with a blood lead level of 5 mcg/dL or higher must undergo continued monitoring for cognitive or behavioral manifestations of lead toxicity indefinitely.10 An elevated blood lead level should be confirmed within 1 to 3 months.4 The CDC recommends that pregnant and lactating women be screened as well, and subsequently any infant whose mother has a blood lead level of 5 mcg/dL or higher.5