APPENDIX C

ANALYTICAL METHODS FOR BLOOD LEAD MEASUREMENT

ROBERT L. JONES*

Lead is one of the most ubiquitous environmental contaminants in the modern world. It is therefore very important that the laboratory and the people collecting the blood lead samples be very aware of the extreme potential for contamination. One of the most important aspects of the laboratory is that the laboratorians must communicate with the people collecting the samples and make them aware of the high potential for contamination. In Expanded Program on Immunization (EPI) studies, if the samples are collected incorrectly, the entire study could be compromised.

In controlled studies it is imperative that the laboratory prescreen the blood sample containers AND the collection devices such as the butterflies, syringes, needles, and the like for lead contamination. If the laboratory cannot prescreen the blood collection devices, then the persons collecting the blood should use “lead-free” collection devices.

Two kinds of whole blood specimens are usually presented to the laboratory —microsamples (capillary or “microtainer,” less than 0.5 ml) and macrosamples (“Vacutainer,” 2 ml or greater). In either case, one key consideration is lot testing of the collection containers themselves, as well as any other devices that directly contact the specimen (for example, needles, cotton gauze swabs, “butterfly” blood collectors, and the like). A copy of the U.S. Centers for Disease Control and Prevention (CDC) procedures for lot testing is available for additional information on lot testing. Microsamples are more likely to clot, and any collected in glass capillaries (not recommended for safety considerations) are inherently more difficult to sample. In all cases it is recommended that whole blood be preserved with EDTA (heparin will work but is more prone to microclots), and shipped and stored at 4°C. The use of filter paper blood collection is not recommended at this time because of the very high potential for environ-

*

Centers for Disease Control and Prevention (CDC), Atlanta, Georgia.



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LEAD IN THE AMERICAS: A call for action APPENDIX C ANALYTICAL METHODS FOR BLOOD LEAD MEASUREMENT ROBERT L. JONES* Lead is one of the most ubiquitous environmental contaminants in the modern world. It is therefore very important that the laboratory and the people collecting the blood lead samples be very aware of the extreme potential for contamination. One of the most important aspects of the laboratory is that the laboratorians must communicate with the people collecting the samples and make them aware of the high potential for contamination. In Expanded Program on Immunization (EPI) studies, if the samples are collected incorrectly, the entire study could be compromised. In controlled studies it is imperative that the laboratory prescreen the blood sample containers AND the collection devices such as the butterflies, syringes, needles, and the like for lead contamination. If the laboratory cannot prescreen the blood collection devices, then the persons collecting the blood should use “lead-free” collection devices. Two kinds of whole blood specimens are usually presented to the laboratory —microsamples (capillary or “microtainer,” less than 0.5 ml) and macrosamples (“Vacutainer,” 2 ml or greater). In either case, one key consideration is lot testing of the collection containers themselves, as well as any other devices that directly contact the specimen (for example, needles, cotton gauze swabs, “butterfly” blood collectors, and the like). A copy of the U.S. Centers for Disease Control and Prevention (CDC) procedures for lot testing is available for additional information on lot testing. Microsamples are more likely to clot, and any collected in glass capillaries (not recommended for safety considerations) are inherently more difficult to sample. In all cases it is recommended that whole blood be preserved with EDTA (heparin will work but is more prone to microclots), and shipped and stored at 4°C. The use of filter paper blood collection is not recommended at this time because of the very high potential for environ- * Centers for Disease Control and Prevention (CDC), Atlanta, Georgia.

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LEAD IN THE AMERICAS: A call for action mental contamination and the resulting unacceptable rate of false positives. When the blood is collected, from either a fingerstick or venous, the hands or the arm of the child or adult must be properly washed, and the person collecting the specimen should be wearing powder-free gloves. There are two main analytical procedures for analyzing the blood, Anodic Stripping Voltammetry (ASV) or Graphite Furnace Atomic Absorption Spectroscopy (GFAAS). GFAAS has been vastly improved by the development of new instruments with microprocessor control; user-friendly, windowed software; capability for automated operation; improved background correction; and improved tube heating. Instruments that use ASV have also been improved, such as the ESA model 3010B, which is easier to use and is more precise and accurate, with lower detection limits than its predecessor. Several key factors should be examined in selecting the appropriate analytical method for your application. These include (but are not limited to): budget, personnel (availability, background, and experience), existing computer climate, throughput (the number of specimens to be processed and reported per unit of time), the need to analyze for elements other than lead, specimen volume available, specimen matrix, and available bench space. Other issues that influence the decision on the analytical method or the instrument manufacturer is the availability of parts and service personnel. Budget considerations are that ASV instruments cost on the order of US$15,000 per unit, and you MUST purchase the reagents from the instrument manufacturer. GFAAS instruments cost US$30,000–60,000 per instrument. Therefore, ASV has a lower initial cost, but has higher reagent costs; GFAAS has a higher initial cost, but lower reagent and gas costs. ASV is manual operation only, whereas GFAAS is normally automated. Another consideration in determining the method to use is whether there will be totally centralized testing or distributed testing. the ASV instrument is capable of being set up at various sites, whereas the GFAAS instrument is not capable of being moved to multiple locations. The need for a steady supply of Ar gas for the GFAAS is also a consideration. A supply of “lead-free” reagents and supplies (water, sample cups, pipets, standards, acids, and the like) must be obtained. A critical component of any blood lead laboratory is the quality assurance (QA) and quality control (QC). Various well-established reference laboratories recommend that the instrument standards be NIST (National Institute of Standards and Technology) traceable. The instrument should be calibrated using multiple standards that cover the appropriate analytical

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LEAD IN THE AMERICAS: A call for action range. Multiple QC materials should be used (commercially available or NIST traceable) to check each analytical ran. A minimum of two QC materials should be used, a “normal” and an “elevated” value. Numerous blood lead laboratories suggest a “low,” “normal, and “high” QC material at the beginning and at the end of the analytical ran, as well as some periodically throughout the run. Many laboratories will evaluate quality with an internal system (bench and blind QC materials as above), as well as participate in an “external” QA/QC system. Examples of these external systems are the CDC/WI Proficiency Testing (PT) Program, the New York State PT program, The College of American Pathologists PT program, or the CDC lab standardization program (Blood Lead Laboratory Reference System BLLRS). Accuracy in determination of lead in these external programs is often the basis of laboratory certification. Reporting requirements should be considered. Most of the GFAAS instruments are microcomputer-controlled and would allow for electronic uploading and reporting of data.

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