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Screening & Diagnosis

Dr. Xingquan Zheng

Introduction

Lead and its compounds exist universally. Because of their adverse health effects, especially on children, they have been some of the most important pollutants impacting human beings. Since 1981, The Institute of Environmental Health Monitoring, Chinese academy for preventive medicine, as an institute under the Ministry of Public Health, has focused attention on monitoring lead pollution, its prevention and in adopting countermeasures against the hazardous effect of lead. Blood lead level is still the best and most sensitive biomarker for identifying lead pollution, human exposure and its adverse effects. As early as in 1972, there were reports referring blood lead levels in the general population in China, but quality assurance procedures were not taken, and hence, the reliability of results was not assured. To determine the status of lead pollution in living environment and human exposure in China, a nationwide blood lead screening program has been conducted since 1983. In this program, a strictly quality assurance procedure was taken as that in WHO/UNEP's global biological monitoring program to ensure that the results would be accurate and comparable. The following are what we did in a screening project and the results that were obtained from the study. Organization and Quality Control in Blood Lead Screening Project

1. Studies on the preparations of quality control samples for blood lead analysis

The analytical results of blood lead usually are over-reported due to contamination of equipment in sampling and analysis. To ensure the accuracy of results, we prepared a set of quality control (QC) samples with bovine blood that consist of 23 lead levels. three of them have been approved by State Bureau of Technical Supervision as certified reference material (GBW 09132~GBW 09134), which can be used publicly as interior quality control (IQC) samples (Table 1). The other 20 are used as external (blind) quality control (EQC) samples. Table 1 Certified lead and cadmium values of bovine blood

2. compile a detailed protocol for blood lead monitoring project. To standardize the methods and procedures in sampling of target populations, collecting blood samples, the quality control in analytical phase and data treatment, a detailed protocol was designed.

3. training

A training course was conducted for responsible staffs from each city or investigation site involved. The content of this course included:

a. purpose and significance of this project.

b. method of sampling target population.

c. method of collecting blood sample.

d methods for avoidance of contamination during blood sampling and analysis and

their importance.

e. the procedure and the requirements of quality control in analytical phase. f. the method of determination of blood lead.

g. data treatment and report

4. questionnaire A standard questionnaire was filled in by the participants or interviewer and used as a basic questionnaire for each city and investigated site selected, but it might be slightly modified, if necessary, with permission by the central organizer.

5. Quality control in analytical phase

Quality control of analytical results was accomplished through analyzing the EQC (unknown to analysts) together with test samples. When the project started, 3~5 sets of quality control blood samples were analyzed. Each set of QC sample consisted of 6 EQC and 2 IQC blood samples with different lead levels. By communicating the evaluation report of the analytical results and by giving technical instructions, the accuracy of the analytical results was improved. During the analysis of the true samples, each batch (50~70) of test sample together with one set of quality control blood were analyzed in the following sequence (Fig.1). The results of QC blood analyzed were sent to us for evaluation.

Fig. 1 the analytical sequence Since the EQC were analyzed as unknown samples together with the test samples, the accuracy of results from the EQC reflected the accuracy of those from test samples. If the results from EQC samples could not meet the criteria for acceptance, the entire process of analysis had to be repeated.

Blood Lead Levels (PbB) of General Populations in China

Fig 1 shows the PbB levels of non-smoking women in various regions of China during 1986~1988. Here we only presents the results from non-smoking women because they best reflect the status of lead pollution in the living environment, without the influence of smoking and their lead burden being transferred to new born infants directly. According to this survey, the blood lead level in the city ranged from 28~112m g/dL, while the total geometric mean of investigated women is 60.6m g/dL. About 8.4% of investigated women had PbB levels over 100m g/L. Fig.2 shows the range of blood lead burden in one city.

It reveals that the average PbB levels was tending to increase with time and there was a sharper increase in the period of 1995~1998 probably due to a rapid increase in the number of vehicles. Table 2 and 3 indicate the range of PbB of preschool children living in urban areas and in small towns, respectively. The percentage of children with PbB levels higher than 100m g/dl were also listed. It indicates that the problem of lead exposure in children is severe, especially the children in small towns where there are many small factories. Table 2: PbB of children living in urban area (mcg/dl)

Table 3: PbB of children living in small town (mcg/dl)

Table 4 shows the range of PbB with age in a group of infants from 0 month (unbilical blood) to 24 months old in Beijing. It indicates that their PbB was increasing steadily with growth, and with the highest PbB at 24 months old. This might be due to infants consuming more food and becoming more active with age. foods usually have higher lead content than milk does, and 24-month old infants may have more chance to contact with dust, which contains very high concentration of lead. Table 4: Range of PbB vs. age (mcg/dl)

PbB screening is only the first step in prevention of the hazardous effects of lead pollution. Numerous unsolved problems are still facing us before we can successfully protect children from lead pollution. Coordination including information exchange is urgently needed between scientists from different countries.

References

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