Analytical considerations in the clinical laboratory assessment of metals

Development and validation of a biomonitoring method to measure As, Cr, and Ni in human urine samples by ICP-UCT-MS

We developed an inductively coupled plasma mass spectrometry (ICP-MS) method using Universal Cell Technology (UCT) with a PerkinElmer NexION ICP-MS, to measure arsenic (As), chromium (Cr), and nickel (Ni) in human urine samples. The advancements of the UCT allowed us to expand the calibration range to make the method applicable for both low concentrations of biomonitoring applications and high concentrations that may be observed from acute exposures and emergency response. Our method analyzes As and Ni in kinetic energy discrimination (KED) mode with helium (He) gas, and Cr in dynamic reaction cell (DRC) mode with ammonia (NH₃) gas. The combination of these elements is challenging because a carbon source, ethanol (EtOH), is required for normalization of As ionization in urine samples, which creates a spectral overlap (⁴⁰Ar¹²C⁺) on ⁵²Cr. This method additionally improved lab efficiency by combining elements from two of our previously published methods(Jarrett et al., 2007; Quarles et al., 2014) allowing us to measure Cr and Ni concentrations in urine samples collected as part of the National Health and Nutrition Examination Survey (NHANES) beginning with the 2017-2018 survey cycle. We present our rigorous validation of the method selectivity and accuracy using National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM), precision using in-house prepared quality control materials, and a discussion of the use of a modified UCT, a BioUCell, to address an ion transmission phenomenon we observed on the NexION 300 platform when using higher elemental concentrations and high cell gas pressures. The rugged method detection limits, calculated from measurements in more than 60 runs, for As, Cr, and Ni are 0.23 μg L-1, 0.19 μg L-1, and 0.31 μg L-1, respectively.

Predictors of urinary and blood Metal(loid) concentrations among pregnant women in Northern Puerto Rico

Given the potential adverse health effects related to toxic trace metal exposure and insufficient or excessive levels of essential trace metals in pregnant women and their fetuses, the present study characterizes biomarkers of metal and metalloid exposure at repeated time points during pregnancy among women in Puerto Rico. We recruited 1040 pregnant women from prenatal clinics and collected urine, blood, and questionnaire data on demographics, product use, food consumption, and water usage at up to three visits. All samples were analyzed for 16 metal(loid)s: arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), cesium (Cs), copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), titanium (Ti), uranium (U), vanadium (V), and zinc (Zn). Urine samples were additionally analyzed for molybdenum (Mo), platinum (Pt), antimony (Sb), tin (Sn), and tungsten (W). Mean concentrations of most metal(loid)s were higher among participants compared to the general US female population. We found weak to moderate correlations for inter-matrix comparisons, and moderate to strong correlations between several metal(loid)s measured within each biological matrix. Blood concentrations of Cu, Zn, Mn, Hg, and Pb were shown to reflect reliable biomarkers of exposure. For other metals, repeated samples are recommended for exposure assessment in epidemiology studies. Predictors of metal(loid) biomarkers included fish and rice consumption (urinary As), fish and canned food (blood Hg), drinking public water (blood Pb), smoking (blood Cd), and iron/folic acid supplement use (urinary Cs, Mo, and Sb). Characterization of metal(loid) biomarker variation over time and between matrices, and identification of important exposure sources, may inform future epidemiology studies and exposure reduction strategies.

Heavy Metal Exposure and Metabolic Syndrome: Evidence from Human and Model System Studies

PURPOSE OF REVIEW

Metabolic syndrome (MS) describes the co-occurrence of conditions that increase one's risk for heart disease and other disorders such as diabetes and stroke. The worldwide increase in the prevalence of MS cannot be fully explained by lifestyle factors such as sedentary behavior and caloric intake alone. Environmental exposures, such as heavy metals, have been implicated, but results are conflicting and possible mechanisms remain unclear. To assess recent progress in determining a possible role between heavy metal exposure and MS, we reviewed epidemiological and model system data for cadmium (Cd), lead (Pb), and mercury (Hg) from the last decade.

RECENT FINDINGS

Data from 36 epidemiological studies involving 17 unique countries/regions and 13 studies leveraging model systems are included in this review. Epidemiological and model system studies support a possible association between heavy metal exposure and MS or comorbid conditions; however, results remain conflicting. Epidemiological studies were predominantly cross-sectional and collectively, they highlight a global interest in this question and reveal evidence of differential susceptibility by sex and age to heavy metal exposures. In vivo studies in rats and mice and in vitro cell-based assays provide insights into potential mechanisms of action relevant to MS including altered regulation of lipid and glucose homeostasis, adipogenesis, and oxidative stress. Heavy metal exposure may contribute to MS or comorbid conditions; however, available data are conflicting. Causal inference remains challenging as epidemiological data are largely cross-sectional; and variation in study design, including samples used for heavy metal measurements, age of subjects at which MS outcomes are measured; the scope and treatment of confounding factors; and the population demographics vary widely. Prospective studies, standardization or increased consistency across study designs and reporting, and consideration of molecular mechanisms informed by model system studies are needed to better assess potential causal links between heavy metal exposure and MS.

Trace Metals Screening Process of Devices Used for the Collection, Analysis, and Storage of Biological Specimens

The Centers for Disease Control and Prevention's (CDC) Environmental Health Laboratory uses modified versions of inductively coupled plasma mass spectrometry (ICP-MS) analytical methods to quantify metals contamination present in items that will come into contact with patient samples during the pre-analytical, analytical, and post-analytical stages. This lot screening process allows us to reduce the likelihood of introducing contamination which can lead to falsely elevated results. This is particularly important when looking at biomonitoring levels in humans which tend to be near the limit of detection of many methods. The fundamental requirements for a lot screening program in terms of facilities and processes are presented along with a discussion of sample preparation techniques used for lot screening. The criteria used to evaluate the lot screening data to determine the acceptability of a particular manufacturing lot is presented as well. As a result of lot testing, unsuitable manufactured lots are identified and excluded from use.

Aluminum Toxicity: Evaluation of 16-Year Trend Among 14 919 Patients and 45 480 Results

CONTEXT

- Annual monitoring with serum aluminum measurements is recommended for dialysis patients who are susceptible to toxic accumulation from contaminated dialysis fluid or from ingestion of aluminum-containing medications.

OBJECTIVE

- To evaluate long-term trends in serum aluminum concentrations and frequency of chronic toxicity.

DESIGN

- A retrospective observational study was conducted by analyzing serum aluminum results obtained from the Veterans Affairs corporate data warehouse. Serum aluminum concentrations of 60 μg/L or greater were considered false positives and not indicative of chronic toxicity if another specimen retested within 45 days had a concentration below 20 μg/L.

RESULTS

- A total of 45 480 serum aluminum results involving 14 919 patients and 119 Veteran Affairs facilities during a 16-year period ending in October 2016 were evaluated. The percentage of elevated (≥20 μg/L) serum aluminum results declined from 31.5% in 2000 to 2.0% in 2015. Average testing intervals changed from every 159 days in 2000 to every 238 days in 2015. Of 529 patients with serum aluminum concentrations of 60 μg/L or greater, 216 (40.8%) were retested within 45 days (average = 21 days); of these, 83 (38.4%) had concentrations below 20 μg/L after repeated measurements. Retesting rates increased with higher initial serum aluminum concentrations.

CONCLUSIONS

- Aluminum toxicity, as assessed by serum levels, has substantially declined over time and is now rare. Many serum aluminum concentrations in the toxic range were not confirmed after retesting. Patients with toxic serum aluminum concentrations should be retested with another specimen before undergoing treatment or investigating sources of exposure to verify abnormal results.