50 Retrospective Analysis of Blood Lead Levels in US Population: Assessing the Role of a National Reference Laboratory in Monitoring and Predicting Lead Contamination Events

Abstract

Background: Lead exposure adversely affects cognitive, behavioral, and psychological development, particularly in children. In adults, occupational or environmental lead poisoning can cause nervous system toxicity, renal dysfunction, and hypertension, but the early symptoms are often nonspecifc. Blood lead level (BLL) measurements assess cumulative lead exposure and are widely used as lead poisoning indicators. In addition to individuals at risk for lead poisoning, the Centers for Disease Control and Prevention (CDC) recommend screening of BLL in children based on risk assessment. In 2012, the CDC reduced the criteria for elevated BLL from 10 ug/dL to 5 ug/dL for children under the age of 6. No level of lead is considered to be safe in children. Therefore, evidence-based improvements on the criteria for evaluating elevated BLL can ensure the continuous decline of BLL and assist with monitoring and prevention of lead contamination events. Method(s): We reviewed data generated by ICP-MS and reported by ARUP Laboratories over a period of seven years (2010-2016) for lead, ordered individually (88.2% of total tests) or as a component of the HYMET blood panel (As, Cd, Pb, Hg; 11.8%). Test positivity defned as BLL =2 ug/dL, geometric mean of BLL at 95% confdence intervals (CIs), percent BLL results =5 ug/dL and =10 ug/dL were stratifed by age, gender, or geographic location. Additionally, we evaluated data reported for Flint, Michigan, before (2010-2013) and after (2015-2016) drinking water crisis using similar metrics. Result(s): The positivity rates of lead testing in children following the CDC switch to 5 ug/dL actionable BLL were 19.3%-16.8% (2013-2016) compared to 23.8%-23.2% (2010-2011). Similarly, percent BLL results =5 ug/dL and =10 ug/dL decreased from 5.5%-6.1% (2010-2011) to 5.6%-5.2% (2013-2016) and 2.1%-2.2% (2010-2011) to 1.9%-1.6% (2013-2016), respectively. The geometric mean of BLL for all populations showed a slight increase over the last seven years, with values ranging from 3.79 ug/dL (2010) to 4.08 ug/dL (2016). In children (=5 years old) a steady increase from 3.69 ug/dL (2010) to 4.05 ug/dL (2016) was also observed. BLL was higher in men (3.92-4.26 ug/dL) than women (3.61-3.84 ug/dL) with men accounting for 62.8%-68.7% of BLL results =5 ug/dL and =10 ug/dL, respectively. Finally, the highest percentage of BLL results =5 ug/dL and geometric mean BLL (6%, 4.46 ug/dL) for the Flint population was observed in 2014, consistent with the water source switch, compared to 2010-2013 (2.4%-2.1%, 3.07-2.95 ug/dL) and 2015-2016 (3.0%-0.9%, 3.53-3.02 ug/dL). Conclusion(s): The decision by the CDC to implement 5 ug/dL as actionable BLL lowered the positivity rates and also the percent BLL results =5 ug/dL and =10 ug/dL. The small increase in the geometric mean BLL indicates previously unrecognized lead exposure that might have been missed using a 10 ug/dL BLL. Our study highlights the role of a national reference laboratory in recognizing and monitoring lead contamination events.