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.
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.
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 µmol/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.
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.