Lead is a naturally occurring heavy metal that exists in both organic and inorganic forms. While recent data have shown a decline in the prevalence of high blood lead levels (BLL) in the developed countries, lead poisoning remains a major public health concern globally with long-lasting adverse health and behavioral effects. In the 2007-2010 National Health and Nutrition Examination Survey (NHANES), the estimate of the mean blood lead level in the U.S. was 1.3 µg/dL, which was a 90% decrease compared to the 1976-1980 NHANES 12.8 µg/dL estimate. An analysis of the 2009 – 2015 NHANES survey, which included 3.8 million venous blood samples from children 6 years old or younger, revealed that around 3% of children exhibited blood lead levels ≥ 5 µg/dL. Risk factors such as living in an area with a high proportion of pre-1950 housing construction, belonging to low-income families were found to be associated with higher BLLs. In addition, race and ethnicity also are predictive of high lead levels, with the greatest risk being in the non-Hispanic black population. The Centers for Disease Control and Prevention (CDC) uses the NHANES 97.5th BLL percentile of 5 µg /dL as an upper reference interval threshold to identify both children and adults with elevated blood lead levels. The U.S. Occupational Safety and Health Administration (OSHA) Lead Standards require workers to be removed from lead exposure when BLLs are ≥ 50 µg/dL (construction industry) or 60 µg/dL (general industry) and allow workers to return to work when the BLL is below 40 µg/dL. While chelation therapy is a mainstay intervention for children with confirmed BLLs ≥ 45 µg/dL, it should be used with caution.
A number of laboratory methods are available to determine BLL. Currently, the well-known technologies are Magellan Diagnostics LeadCare Testing Systems, flame atomic absorption spectrometry (FAA), electrothermal atomic absorption spectrometry (also referred to as graphite furnace atomic absorption spectrometry, GFAA), and inductively-coupled plasma mass spectrometry (ICP-MS).
The CLIA-waived LeadCare Testing Systems are popular because they have a portable size, employ an electronic calibration and simple procedures, use disposable consumables, and can generate results for capillary blood specimens in a few minutes for physician’s offices or smaller clinical laboratory settings. However, effective April 2017, Magellan Diagnostics notified customers that the LeadCare Testing Systems may underestimate the blood lead levels and give inaccurate results when processing venous blood. The Food and Drug Administration (FDA) issued a Class I product warning to laboratories and health care professionals that they should not use any Magellan Diagnostics’ LeadCare device for testing venous blood specimens.
Atomic absorption (AA) methods have long been the mainstay for blood lead testing. AA uses the principle of generating ground-state free atoms in a flame (FAA) or a graphite-coated furnace (GFAA), and measuring the amount of light absorbed from a wavelength-specific light source. The most common application of FAA in lead testing is to analyze dried blood spots on filter paper with no preliminary sample preparation. The analytical principle of GFAA is the same as FAA, except that the FAA flame is replaced by a small GFAA heated graphite tube. Most laboratories have replaced FAA with GFAA due to improved sensitivity and lower specimen volume requirements. GFAA technology has sub-ppb to ppb (parts per billions, ppb = µg/L) sensitivity, relatively narrow dynamic range, and low throughput. It is a single element technique which measures only one analyte at a time.
ICP-MS uses a high temperature plasma discharge to generate positively charged ions that are measured for the mass-to-charge (m/z) ratio by mass spectrometry. ICP-MS is a rapid ultra-trace multi-element technique. It has a parts-per-trillion (ppt = ng/L) sensitivity, a wide dynamic range of 8 orders of magnitude, and high throughput. ICP-MS can measure multiple elements simultaneously, and has a unique capability to perform isotopic analysis and speciation analysis. Due to its multi-element capability, higher sample throughput and higher sensitivity, ICP-MS has become the method of choice for many reference laboratories. Yet it is a high complexity methodology and requires more technical expertise by the operator, therefore may not be suitable for every laboratory. In addition, capital and operational cost is another factor to be considered. A thorough evaluation and planning process is needed to determine the suitable methodology and device for blood lead testing in each laboratory.