4. Medical surveillance of employees is often an important addition to the control measures in the workplace, regulation 7(1) of the HCS Regulations specifies where medical surveillance is appropriate for the protection of the health of employees.
4.1 MEDICAL SURVEILLANCE
Medical surveillance is defined in the Regulations to cover the spectrum of potential effects of an HCS on an employee, from absorption of the substances through to clinical disease. Medical surveillance may be grouped broadly into-
a. biological monitoring, to measure the extent of absorption of an HCS by the employee.
b. medical screening, to detect any adverse affects of an HCS on the employee.
4.2 BIOLOGICAL MONITORING OF EXPOSURE
4.2.1 Objectives
Biological monitoring of exposure can be divided into two types of testing:
a. Biological monitoring: Measures the bio-chemical concentrations of HCSs and/or their metabolites in biological samples of exposed individuals, e.g. blood lead for inorganic lead exposure, or urinary arsenic for inorganic arsenic exposure. The aim is to measure the degree of absorption into the body by measuring indicators in representative biological samples, typically urine or blood (usually nor related to the target organ).
b. Biological effect monitoring: Determines the intensity of biochemical or physiological change due to exposure, e.g. red cell cholinesterase for exposure to organosphosphate pesticides, or zinc protoporphyrin (ZPP) for exposure to inorganic lead.
4.2.2 Uses of biological monitoring
Biological monitoring tests are indices of an individuals exposure and they may be a useful tool for the occupational health and safety team. They give information on the overall level of exposure, regardless of whether an HCS has been absorbed by the respiratory, oral, or cutaneous route. Cutaneous absorbtion can play a significant role in the case of some organic compounds. The amounts absorbed through the skin may be comparable to or even higher than those absorbed via the respiratory tract.
Where appropriate, environmental control measures may thus be supplemented, with biological monitoring. Knowledge of the real individual exposure permits targeted applications of preventive measures.
4.2.3 Important considerations in biological monitoring
a. In choosing a test to meet the above objectives, it is important to have an understanding of the relationship between environmental exposure and the concentration of an HCS in biological samples. This includes an understanding of the principles of absorption, biotransformation, distribution and excretion of an HCS.
b. In addition, there should be analytical methods available of sufficient sensitivity and specificity to detect concentrations of the substance in urine, blood or exhaled air in the range likely to be encountered in industry.
c. The HCSs listed in Table 3 of Annexure 1 are those for which the above criteria have a reasonable chance of being met.
4.2.4 Biological Exposure Indices (BEIs)
BEIs are reference values intended as guidelines for the evaluation of potential health hazards in the practice of industrial hygiene. A BEI represents in theory the level of an HCS or metabolite most likely to be observed in a specimen collected from a healthy worker who has been exposed to an HCS to the same extent as the worker with inhalation exposure to an OEL-TWA. BEIs do not represent a sharp distinction between hazardous and non-hazardous exposures. For example, owing to biological variability, it is possible that an individuals measurements can exceed the BEI without incurring an increased health risk. Conversely, there may be some susceptible individuals who may be harmed at effects below the BEI.
If measurements in specimens obtained from a worker on different occasions persistently exceed the BEI, or if the majority of measurements in specimens obtained from a group of workers at the same workplace exceed the BEI, the cause of the excessive values must be investigated and proper action be taken to reduce the exposure.
BEIs apply to eight-hour exposures, five days a week. However, BEIs for differing work schedules may be extrapolated on pharmacokinetic grounds. BEIs should not be applied either directly or through a conversion factor, in the determination of safe levels for non-occupational exposure to air and water pollutants, or food contaminants. The BEIs are not intended for use as a measure of adverse effects or for diagnosis of occupational illness.
4.3 MEDICAL SCREENING
4.3.1 Objectives
a. The principle of general medical screening is to detect a disease at an early subclinical or presymptomatic stage in order to take action to reverse these effects or to slow progression of the disease. The abnormalities sought, include pathophysiological or histopathological changes. Such tests are well established in general preventative medicine, e.g. PAP smears for cervical cancer, cholesterol screening, feacal occult blood for lower bowel cancer, etc.
b. In medical surveillance in industry one is interested not only in detecting adverse effects in the individual, but also in the implication of the findings for the effectiveness of workplace control measures., Medical surveillance is thus directed not only at early adverse effects but also at established disease.
4.3.2 Types of examination
a. The number of validated screening tests with regard to HCSs is smaller than in general preventive medicine, but is likely to grow in the future. Examples of subclinical tests include urinary cytology for bladder cancer among workers exposed to potential bladder carcinogens, or full blood counts for employees exposed to an HCS toxic for the bloodforming organs.
b. Medical surveillance may include simple clinical examination, such as examination of the skin of employees exposed to contact irritants or allergens, or of the nasal septum of employees exposed to chromates.
c. Chest X-rays for silicosis are an example of screening for irreversible (although potentially progressive) disease. Lung function testing is well established as a non-specific test for the possible effect of respiratory irritants, sensitisers and fibrogenic agents.
4.4 DESIGNING AND IMPLEMENTING A PROGRAMME OF MEDICAL SURVEILLANCE
4.4.1 The following steps should be included in any programme:
a. Risk assessment to determine the potential exposure to and routes of absorption of an HCS, as required by regulation 5.
b. Identification of target-organ toxicity, so as to direct medical screening.
c. Selection of appropriate tests and testing schedule. Tests should have the desirable operating characteristics of high sensitivity, specificity, reliability and predictive value. The frequency of testing is laid down in general terms by regulation 7(2) , but should in any case be based on an understanding of the nature of the hazard and the natural history of any adverse effects.
d. Development of action criteria. These are provided for some HCSs in the form of BEIs in Table 3 of Annexure 1. Criteria for interpreting lung function testing have also been published in the medical literature. However, in many cases, the occupational health practitioners will have to develop pragmatic criteria in the context of the specific workplace.
e. Standardisation of test process. Quality control needs to be exercised both in the testing site and in the laboratory contracted to carry out analyses. Consistency over time should be sought so as to make longitudinal measurements comparable.
f. Ethical considerations. Information and training of employees as required by regulation 3 (1) should include the rationale for doing medical surveillance, and the consequence of abnormal findings. An employee must be notified of the results and interpretation of his/her tests and any recommendations made. The confidentiality of personal medical records is laid down by regulation 9.
g. Determination of employees fitness to remain in that job. [Regulation 7(3) ]. Results may be compared against the action criteria (BEI if relevant), and preferably also the employees previous results to determine whether individual action needs to be taken. Action may include repeating the test, further medical examination, removal of the employee from further exposure, and notification of the employer. Co-operation of employees can be best secured by a policy of protection of conditions of service in case of medical removal from a particular job.
h. Evaluation of control. An abnormal finding in an employee, or a pattern of findings in a group of employees, may point to inadequate primary control of exposure. In such cases the employer needs to be notified of such details of the medical findings as are necessary to evaluate the workplace problem and take remedial action.
i. Record keeping. This includes both medical records and exposure information for every employee. While the employer is responsible for record keeping in terms of regulation 9, the contents of personal medical records may be accessible to the occupational medicine practitioner, the employee, and any person nominated by the employee in writing.
4.4.2 The onus is on the occupational health practitioner carrying out medical surveillance to be familiar with the latest scientific information regarding the HCS and tests that might be useful. The aim should be to design a programme that is rational, ethical and effective. This may have to be done in the face of incomplete information of uncertainty regarding exposures, toxicity and test performance.