to the editor: The article by Drs. Staudinger and Roth on occupational lead poisoning1 was timely and comprehensive. The authors' observation that a high index of suspicion is necessary to avoid missing the diagnosis cannot be emphasized enough.
One finding that should prompt consideration of occupational lead poisoning is unexplained basophilic stippling of the red cells on peripheral blood smear. The stippling seen in this condition is usually coarse,as opposed to the fine stippling seen in hemorrhage or hemolysis. A comprehensive occupational history, as well as the more specific studies listed in the article, should be pursued routinely as a follow-up to this important finding. It could save lives.2
to the editor: We congratulate Drs. Staudinger and Roth on an excellent review of occupational lead poisoning, which includes user-friendly resource lists.1 As physicians at the Occupational Safety and Health Administration (OSHA), we have encountered problems if lead screening guidelines are provided in rote fashion based solely on the levels of lead permitted by OSHA's lead standard. We have encountered the following situations:
Physicians who clear patients to work with lead because their blood lead levels have not reached the mandatory cut-off level, despite significantly elevated levels of zinc protoporphyrin and mild anemia.
Elevated levels of zinc protoporphyrin, with or without declines in hematocrit levels, that have not been followed up to rule out possible iron deficiency.
Blood lead levels in young patients that have risen from less than 5 μg per dL (0.25 μmol per L) to over 30 μg per dL (1.45 μmol per L) without comment from the examining physician.
Situations in which there is almost no communication between the safety officer and the examining physician, or in which the examining physician provides the entire medical examination report to a nonmedical safety officer.
Measurement of whole blood lead levels is an extremely accurate method of evaluating current exposure to lead. The levels permitted by the OSHA standard resulted from a great deal of compromise and have not been revised since the publication of the standard in 1978. The level at which overt toxicity occurs remains controversial, and the levels that are in the OSHA standard do not guarantee the absence of lead toxicity.2
The most serious concern about long-term lead toxicity in the range experienced by current employees (i.e., generally less than 40 μg per dL [1.95 μmol per L]) is the potential for nephrotoxicity. For this reason, efforts should be made to identify individuals at risk for renal damage from other occupational exposures (such as cadmium) and from nonoccupational causes (such as diabetes or hypertension), and to cautiously monitor their lead exposure. The physician may wish to contact the environmental safety manager at the plant to find out if additional industrial hygiene measures may be useful. For example, powered air purifying respirators provide additional protection compared with the usual negative pressure respirators used by most employees, and their use may be warranted in these individuals. While making any recommendation, it is important to maintain medical confidentiality, including the nature of medical conditions that are non–work-related. The information to be shared with the employer is that the individual is being cleared for work, with certain specific restrictions.
Another area of significant concern is reproductive toxicity due to exposure to lead. Under the OSHA standard, medical examination or consultation may be requested by an employee who desires information about reproduction and exposure to lead. For men, we generally recommend a three-month medical removal from lead exposure before conception is attempted. We recommend medical removal protection for women throughout pregnancy since the fetus is more susceptible than the general pediatric population, for whom the level of concern is a blood lead level of 10 μg per dL (0.5 μmol per L), and it is difficult to achieve these levels in many industrial and construction settings. Medical removal protection maintains job security and income for up to 18 months while individuals are transferred to jobs without exposure to lead.
Please bear in mind that the level of lead in the general population now averages 2.8 μg per dL (0.15 μmol per L).3 When the level of lead in a new employee increases by four or five times, the physician may wish to identify the source of the problem, even if the level remains below 40 μg per dL (1.95 μmol per L).
Finally, we would like to encourage all physicians who conduct any occupational medical surveillance to make use of the environmental safety managers. The goal of medical surveillance is to provide a feedback loop for engineers, industrial hygienists and safety managers to recognize that a breakdown in true primary prevention has occurred, and to identify and correct the problem.
in reply: We wish to thank Drs. Bennett for their insightful observation regarding the finding of basophilic stippling and its possible etiology related to lead. Such a finding may indeed provide the impetus for further questioning regarding occupational exposure to lead, thereby permitting earlier detection of lead poisoning in workers who are at risk and the subsequent institution of protective measures before employees experience adverse clinical effects. As previously stated in our article,1 the diagnosis of clinical effects related to lead requires a high index of suspicion on the part of the examiner and any clues that suggest potential poisoning should be used.
We also thank Dr. Sokas and colleagues for their comments in regard to occupational lead poisoning and the OSHA lead standard. They succinctly define the renal and reproductive concerns, highlighting individuals at potential risk with blood lead levels that are lower than the stated standard. Importantly, they point out that the standard cannot assure the absence of adverse health effects, even if held strictly to its stated blood levels.
From an occupational physician's standpoint, failure to reach the mandatory cut-off levels of blood lead levels does not preclude the need for continued medical surveillance and initiation of proper control measures. Gradually increasing blood lead levels in a worker, with or without overt health effects, require further investigation of both the worker and the work environment. Timely intervention before the attainment of mandatory cut-off levels could provide the controls needed before clinical effects manifest and/or other workers are noted with increased blood lead levels. Importantly, Dr. Sokas and colleagues relate how critical the relationship is between the examining physician and the safety officer for the implementation of proper control measures, both administrative and engineering. This relationship is the key to primary prevention efforts and long-term avoidance of further exposure.