EDTA is essential to recover lead from dried blood spots on filter paper.

Background: Residual dried blood spots (DBSs) on filter paper from neonatal screening have been proposed as samples for population survey of lead contamination. We have investigated the EDTA effect on lead release in the eluting solution.

Methods: Furnace atomic absorption spectrophotometry has been used for lead measurements. Standard, blank and sample solutions contained 2% m/v NH(4)H(2)PO(4), 0.5% v/v Triton X-100 and 0.2% v/v HNO(3) as matrix modifier solution (MMS) with or without EDTA. A calibration curve was established from aqueous standard solutions. Paper discs from DBS and blank, punched near the DBS, were eluted in MM solution and, where required, EDTA at different concentrations. Specimens were leftover DBSs with different storage times, matched samples from 20 adult patients consisting of liquid whole blood (LWB) containing 5 mmol/L EDTA, DBSs eluted in MM solution with 5 mmol/L EDTA or without EDTA.

Results: Optimal lead recovery from DBS required 5 mM EDTA in the eluting solution. Mean lead levels of LWB and DBSs eluted with EDTA were similar and higher than DBSs without EDTA (P<0.001). Without EDTA, the median value of lead optical density was lower for 6-month-old DBSs than for blanks (P<0.001).

Conclusions: Residual DBSs can be used for population survey, but 5 mmol/L EDTA in the extracting solution is required to fully recover lead.