Leaden blood spot

A single drop of blood absorbed on to a filter paper is all that is needed for a new test for lead, based on solid sampling-graphite furnace atomic absorption spectrometry (SS-GFAAS). The minimally-invasive method would allow many more people, and children in particular, to be tested quickly and safely for exposure to lead and to facilitate follow-up industrial safety incidents involving the neurotoxic metal.

The American Academy of Pediatrics (AAP) in 2005 recommended that the US government test all children at least once to obtain a baseline lead exposure level and to identify any children with excess lead exposure and preclude further exposure. Obviously, lead exposure is a global issue rather than one confined to children in the US.

Lead may enter biological systems as lead(II) ions from contaminated soldered food cans, the water supply, from atmospheric and environmental pollution, and the combustion of leaded fuels, as well as dust from lead-containing paints.

Martín Resano, Esperanza García-Ruiz, and Miguel Belarra of the Department of Analytical Chemistry, at the University of Zaragoza, Spain, and L. Rello of the Department of Clinical Biochemistry, at the Miguel Servet Universitary Hospital, also in Zaragoza have now turned to SS-GFAAS to design an almost painless and quick test for lead exposure levels. 

The researchers developed a simple procedure involving a skin-prick to obtain a blood sample on a filter paper, which is then dried and a small blood-bearing disc punched from the filter paper subjected to SS-GFAAS. To validate the approach, the researchers carried out a systematic study of the possible variables, such as total blood volume, putative chromatographic effects on lead distribution on the filter paper, and differences in spread of the blood sample. Using, spiked initially lead-free blood samples for calibration, they found that variations in these parameters within the usual clinical range did not influence significantly the determined lead concentrations of actual samples and certified reference materials.

The team demonstrated a detection limit of 2.5 micrograms of lead per litre, and a working range up to 840 micrograms. Sample throughput is about ten minutes per sample, but the ease of sample collection, transporting and storage together with the low cost of the technique suggest that this approach could be used very effectively to screen children in a short space of time with no great expense, particularly in places where collecting sites might be far away from central laboratories.

"Many people in the clinical community are against the filter paper test for lead," Resano told SpectroscopyNOW, "The goal of our work is to show that, if a suitable direct solid sampling technique such as SS-GFAAS is used (thus avoiding the tedious and contamination-prone step of digestion of the papers), it is feasible to achieve satisfactory results for Pb blood using the filter paper test."