A community outreach lead screening program using capillary blood collected on filter paper

Abstract

Objective: To test whether a method of fingerstick blood sample collection onto filter paper could be used as an alternative screening method in the field in settings where environmental lead contamination is a high risk. Method: Members of the Pediatric Mobile Team of Children's Hospital of Michigan, Detroit, collected paired venous and capillary blood samples from 120 children, aged 6 months to 6 years, who presented for services at any of 7 sites located in decaying neighborhoods of older sections of Detroit. All samples were analyzed for lead content by graphite furnace atomic absorption spectrometry. Results: When filter paper samples with blood lead levels of 0.48 μmol/L (10 μg/dL) or higher were compared with matched venous samples, the concordance coefficient was 0.96. The sensitivity and specificity of the filter paper samples relative to the venous samples for a cutoff of 0.48 μmol/L (10 μg/dL) or higher were 94% and 99%, respectively, with a positive predictive value of 97%. However, at a cutoff of 0.72 pmol/L (15 μg/dL), the sensitivity and specificity dropped to 75% and 98%, respectively, with filter paper samples underreporting blood lead values. At any cutoff point (0.48, 0.72, or 0.96 μmol/L [10, 15, or 20 μg/dL]), the filter paper method was highly specific for lead. Conclusions: Capillary filter paper sampling is an accurate and practical alternative to venous sampling for blood lead screening using 0.48 μmol/L (10 μg/dL) as the cutoff. The filter paper method predicts levels of 0.72 μmol/L (15 μg/dL) or higher less well. The cause of divergent values above 0.72 μmol/L (15 μg/dL) is not clear. Environmental contamination of capillary filter paper, however, does not seem to be an explanation.