Matrix-matched calibrators are necessary for robust and high-quality dried blood spots lead screening assays by inductively coupled plasma-mass spectrometry.

Background and aims: Reliable lead screening methods are necessary to support early identification of lead exposure in children. Sample collection using dried blood spots (DBS) offers advantages compared to traditional venipuncture and capillary collection. Here, we describe and compare three lead DBS inductively coupled plasma-mass spectrometry (ICP-MS) methods for lead screening. Materials and methods: Lead was extracted from Whatman 903 protein saver cards punches and analyzed by ICP-MS across three independent clinical laboratories. Each laboratory evaluated the performance of aqueous and matrix-matched DBS calibrators using external quality control samples (WI State of Laboratory of Hygiene Program). Leftover patient samples (n = 39) were used for an interlaboratory comparison of lead DBS. Lead DBS results were compared to whole blood methods. Results: The DBS ICP-MS methods using matrix-matched DBS calibrators had superior performance to the aqueous calibrations. There was a strong correlation between lead measured in DBS (matrix-matched) and whole blood for the three methods evaluated. Conclusion: Lead can be measured accurately by ICP-MS in DBS samples when matrix-matched calibrators are used. External quality control programs are valuable to assess the performance of DBS methods. DBS lead ICP-MS methods are a robust analytical option for lead screening even though the limitations of DBS are well recognized.

Whole blood selenium determination by inductively coupled plasma mass spectrometry.

OBJECTIVE: To develop a sensitive method for accurately measuring whole blood selenium and determining an appropriate reference interval for the local Cleveland population. DESIGN AND METHODS: The assay was developed and validated on an inductively coupled plasma mass spectrometry (ICP-MS) with a collision cell. Whole blood trace element free EDTA tubes were used to collect samples for the reference interval study (n=50). Samples were collected after at least 8h fast from healthy adults (76% females) with ages between 19 and 64yr. Whole blood aliquots (1mL) in acid washed cryogenic vials were stored at -70°C until analysis. RESULTS: The method passed the matrix effect, interference (except for Gd), and carryover tests. The method had a linear range of 0.2-7.1µmol/L with accuracies of 87.1-118.1%. The total assay imprecision (CV) was <2.5% across the concentration levels tested. Comparison to another ICP-MS assay offered by an independent clinical lab yielded a Deming regression with a slope of 0.98, an intercept of 0.1µmol/L, a standard error of estimate of 0.1µmol/L, a correlation coefficient of 0.9846, and an average difference of 0.8%. The whole blood Se reference interval using a transformed parametric method was 2.2-3.5µmol/L. CONCLUSIONS: This whole blood Se ICP-MS methodology is sensitive and acceptable for patient testing.

Highly sensitive measurement of whole blood chromium by inductively coupled plasma mass spectrometry.

OBJECTIVES: Chromium (Cr), a trace metal element, is implicated in diabetes and cardiovascular disease. A hypochromic state has been associated with poor blood glucose control and unfavorable lipid metabolism. Sensitive and accurate measurement of blood chromium is very important to assess the chromium nutritional status. However, interferents in biological matrices and contamination make the sensitive analysis challenging. The primary goal of this study was to develop a highly sensitive method for quantification of total Cr in whole blood by inductively coupled plasma mass spectrometry (ICP-MS) and to validate the reference interval in a local healthy population. DESIGN AND METHODS: This method was developed on an ICP-MS with a collision/reaction cell. Interference was minimized using both kinetic energy discrimination between the quadrupole and hexapole and a selective collision gas (helium). Reference interval was validated in whole blood samples (n=51) collected in trace element free EDTA tubes from healthy adults (12 males, 39 females), aged 19-64 years (38.8±12.6), after a minimum of 8 h fasting. Blood samples were aliquoted into cryogenic vials and stored at -70 °C until analysis. RESULTS: The assay linearity was 3.42 to 1446.59 nmol/L with an accuracy of 87.7 to 99.8%. The high sensitivity was achieved by minimization of interference through selective kinetic energy discrimination and selective collision using helium. The reference interval for total Cr using a non-parametric method was verified to be 3.92 to 7.48 nmol/L. CONCLUSION: This validated ICP-MS methodology is highly sensitive and selective for measuring total Cr in whole blood.