A-341 Development and Validation of an ICP-MS Method to Quantify Lead in Dried Blood Spots
Authors: Muldrow R A , Torres C , Kaiwusaier K , Martir S , Greene D N 
Published: September 2023

Abstract

Introduction
The CDC estimates that ∼500 000 children in the US between ages 1–5 have unsafe blood lead concentrations (&gt; 3.5 ug/dL). Lead toxicity can affect all bodily systems and can be detrimental to children's developing brains and nervous systems. Since lead exposure does not always induce obvious and immediate symptoms, screening is an essential tool to public health. Recently, there was a point of care device recalled that was used to measure blood lead across the country. The demise of this method left a gap for lead screening nationally. Dried blood spot (DBS) sampling is an excellent alternative to traditional collections as it is cost effective, less contamination prone, less invasive, and is amenable to non-standard collection locations. The objective of this study was to develop an accurate and precise DBS lead method with the intention of improving access to screening in underserved populations.

Methods
Lead was detected using an Agilent7800 ICP-MS. DBS were punched (6mm) and lead was extracted into a water based diluent containing EDTA, ammonium pyrrolidine dithiocarbamate, tetramethylammonium hydroxide, Triton X-100, ethanol and iridium. All DBS were sampled from Whatman903 protein saver cards using a 6mm punch. A 6-point calibration curve was made using custom UTAK whole blood lead controls and a diluent blank (target concentrations: 0, 1, 7, 14, 60 and 100 ug/dL). Exact concentrations of the liquid calibrators were determined using a previously validated lead whole blood method. Once the whole blood calibration concentrations were determined, 40 uL of each calibrator was spotted and allowed to dry for at least 24 hours before a 6mm spot was punched and extracted. Precision was determined using three concentrations of UTAK Whole Blood Lead QC (40 uL/spot; 6mm punch). Each level was run in replicates of five for five days. Linearity was confirmed by running five levels of DBS calibration standards for five days. Accuracy was evaluated using Wisconsin DBS Event Proficiency Testing (PT) Samples and results were compared to the peer means. For the method comparison, venous whole blood samples were collected into Royal Blue EDTA metal free vacutainer tubes; DBS samples were spotted directly from the finger (n = 20). Additional comparison samples (n = 10) were derived from the Pennsylvania whole blood PT program by spotting 40 uL.

Results
The interday precision for the low, mid, and high QC material was 5.0%, 7.5%, and 3.0% at concentrations of 6.8, 20.7, and 35.8 ug/dL, respectively. Lead concentrations from 1.0–100 ug/dL were within the allowable nonlinearity of 1 ug/dL or 5.0% (y = 1.01x-1.6;R = 0.999). Wisconsin DBS PT results (n = 12; range 0.0–38 ug/dL) were accurate within 10% of the peer mean and within acceptability criteria. Comparison of paired whole blood to DBS samples had an average bias of 4.68% (0.31 ug/dL; Y = 1.027x + 0.13(R = 0.999); range 0.1–77.7 ug/dL).

Conclusions
We developed and validated an accurate and precise lead DBS method using matrix-matched calibrators. This method supports that DBS collection may be an adequate sample to screen for lead exposure and could supplement the current need for additional ways to screen underserved and/or remote populations.