To the Editor.
—To achieve the goal of blood lead screening for all children aged 6 months to 6 years,1 testing should be easy to perform, widely available, inexpensive, and reliable. Specimens are more easily obtained from children by fingerstick than by venipuncture. However, increased opportunity for contamination of capillary specimens has raised concerns about their reliability. Dr Schlenker and colleagues2 compared capillary and venous blood lead levels in children and showed that between 0% and 5% (depending on sampling protocol) of the capillary results were false positives and 1% to 8% false negatives.2These percentages were referred to as false-positive and false-negative rates, which may lead to confusion. For example, the term "false-positive rate" traditionally has meant the percentage of false positives in the total positives (false positives/[false positives + true positives]).3 Only this statistic has predictive value for determining the significance of a positive test.
Rainey PM, Schonfeld DJ. Comparability of Capillary and Venous Blood Samples for Lead Screening. JAMA. 1994;272(19):1482. doi:10.1001/jama.1994.03520190024016