Radioimmunoassay screening of dried blood spot materials for benzoylecgonine

Residual samples of blood spots, which are routinely collected on almost all newborns in the United States, can be used to determine seroprevalence information on newborns and maternal exposures to various substances, including drugs of abuse. By modifying a commercial radioimmunoassay (RIA) kit for urinary samples, one can use blood spotted on filter paper as a matrix to quantitate the cocaine metabolite benzoylecgonine (BE). BE is stable for long periods of time in blood spots and we were able to quantitatively extract it with aqueous buffer. There were no matrix effects of the blood spot eluate on the RIA, and excess lipid in the blood did not alter measurement of BE. By using standards made up of BE in negative blood spot eluate and calibrators of blood that were spiked with BE and then spotted on filter paper to determine extraction efficiency, low levels of BE in blood could be measured. The limit of detection was 5 ng/mL, and the limit of quantitation was 10 ng/mL. Levels of BE in blood collected at autopsy in eluates of blood spots were measured, and they established excellent correlation (r2 = 0.93) with gas chromatography/mass spectrometry measurements. To test this technology, residual blood spots on 545 infants from three states were analyzed for BE.