Trends in Blood Lead Levels Quantified by ICP-MS: A Reference

Laboratory Retrospective Study

Since the 1970s, regulatory efforts to ban the use of lead in paints andgasoline has resulted in a significant decline in mean blood lead levels(BLLs) in the United States. Between 1976 and 1991, the mean BLLreported by the National Health and Nutrition Examination Survey(NHANES) decreased from 12.8 to 2.8 μg/dL (1). However, lead toxicityfrom occupational exposure (e.g., mining, construction, and batterymanufacturing industries) and contaminated drinking water (e.g.,water transportation through lead or lead-soldered pipes) remains aconcern. In 2014, an estimated 76,680 children aged <5 years had BLLsbetween 5 - 9 µg/dL in the United States (2). Similarly, about 27,218adults aged ≥16 years had BLLs ≥10 µg/dL in 2012 (3).

Lead is a toxic metal known to cause severe adverse effects includinganemia, renal dysfunction, hypertension, neurologic damage,developmental disorders, and reproductive disorders. Hence, noconcentration of lead in blood is considered safe. In 2012, the Centersfor Disease Control and Prevention (CDC) reduced its blood leadreference value from 10 µg/dL to 5 µg/dL.

Study ObjectiveIn this study, we describe the measurement of lead concentrations invenous whole blood specimens using inductively coupled plasma massspectrometry (ICP-MS). Additionally, a retrospective analysis of patientBLLs reported by ARUP Laboratories was performed to evaluate thepositivity rates of blood lead concentrations greater than 5 µg/dL.

Retrospective Data Analysis Results

Conclusions

Introduction

The described ICP-MS method for quantification of Pb in venous whole bloodwas validated following CLSI guidelines. The linear regression for accuracy was y= 0.9363x + 0.2562 with R2 value of 0.9952 for Pb concentrations in the range of1.2 – 96.6 µg/dL. Linearity across the analytical measurement range (1.1 – 450µg/dL) was acceptable with a slope of 1.003, y-intercept of -0.347, and R2 valueof 1.000. Inter-assay and intra-assay imprecision was < 4% CV for the low andhigh controls. The lower limit of quantification was determined to be 1.75µg/dL.A total of 871,909 (male = 443,412, female = 428,497) venous whole blood Pbresults from patients aged 0 – 95 years were included in the data analysis. BLLs≥5 µg/dL was observed in 37,205 (4.3 %) patients and the mean BLL was 11.4µg/dL. There was a steady decline in Pb positivity between 2012 and 2018(figure 1). Higher blood lead level was observed in patients aged ≥ 18 comparedto patients aged < 18 (figure 2). Similarly, men had higher blood lead levelscompared to women (figure 2).

Nkemakonam C. Okoye1, and Kamisha L. Johnson-Davis1,2

1University of Utah Health Sciences Center, Department of Pathology, Salt Lake City, Utah, USA 2ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah, USA

Methods

Venous whole blood was collected in certified trace-metal free royalblue or tan top collection tubes. A 50 μL aliquot of the blood specimenwas diluted with 950 μL diluent solution containing beryllium (Be),gallium (Ga), yttrium (Y), indium (In), rhodium (Rh), and iridium (Ir) asinternal standards, gold (Au) as stabilizer, 0.1% Triton X-100, 1.75%EDTA, and 1% ammonium hydroxide. The diluted blood specimenswere aspirated into the Agilent 7700 ICP-MS spray chamber using aCETAC MVX-7100 autosampler to form aerosol droplets, which wereatomized and ionized in argon plasma. To combat polyatomicinterferences, analysis was performed in kinetic energy dissociation(KED) mode, with helium gas at 3.0 mL per minute. Ions were filteredby the main quadrupole, transduced into electrons, and magnified byan ion multiplier before being counted and summed by the detector.

A four-point calibration curve ranging from 2 µg/dL to 100 µg/dL wasused for blood lead (208Pb) quantification. Accuracy was evaluated bycomparison to a previous in-house ICP-MS method run in standardmode on a Perkin Elmer DRC II ICP-MS instrument using proficiencytesting samples, spiked patient blood pools, and previously analyzedpatient samples. Imprecision was assessed by measuring replicates oflow (2.3 µg/dL) and high (85.0 µg/dL) spiked blood samples. Linearitywas tested by analyzing four replicates of spiked blood samples(concentration range = 1 – 450 µg/dL) on three different runs. The limitof quantification was evaluated by analyzing four replicates of spikedblood samples at the lowest calibrator concentration over five days.

Retrospective patient results were retrieved from our internallaboratory information system for evaluation of blood lead positivityrates. To avoid duplication of patient data, when multiple tests wereassociated with the same individual within the same calendar year,only the first result was included in this study. The study was approvedby the University of Utah IRB for a limited data set

Method Validation Results

1. Pirkle JL, Brody DJ, Gunter EW, Kramer RA, Paschal DC, Flegal KM, MatteTD. The Decline in Blood Lead Levels in the United States: The NationalHealth and Nutrition Examination Surveys (NHANES). JAMA 1994;272:284-91.

2. Raymond J, Brown MJ. Childhood Blood Lead Levels in Children Aged <5Years - United States, 2009–2014. MMWR Surveillance Summaries2017;66:1–10.

3. Alarcon WA. Elevated Blood Lead Levels Among Employed Adults - UnitedStates, 1994–2012. Morbidity and Mortality Weekly Report (MMWR)2015;54:52-75

References

Acknowledgments

The authors wish to thank Dave Davis for his assistance with data collection, LaurenZuromski for her help with data analysis, and Rebecca Parker for her contribution tothe method validation studies.

y = 0.936x + 0.256R² = 0.995

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Low (µg/dL) 2.04 0.03 1.68% 2.06 0.07 3.14%

High (µg/dL) 80.81 2.01 2.49 % 79.66 2.63 3.30%

N < 100

N/A

Figure 4: Heat mapshowing Pb positivity rate(≥ 5 µg/dL) across UnitedStates for whole bloodspecimens submitted toARUP Laboratories from2012 to 2018

Figure 1: Pb positivity rate (≥ 5 µg/dL) showing linearregression line and 95% confidence interval

Figure 2: Pb positivity rate (≥ 5 µg/dL) in adults(age ≥ 18) and children (age < 18)

Figure 3: Pb positivity rate (≥ 5 µg/dL) in malesand females