Bone lead measurement

The article “Lead and children” by Abelsohn and Sanborn¹ in the June edition of Canadian Family Physician was full of good information for family physicians. As our understanding of the toxicity of lead increases, we have learned of health effects at lower and lower levels of exposure, as Abelsohn and Sanborn make clear. It thus becomes even more important for physicians to not only be able to properly diagnose and treat lead poisoning, but to also be able to recognize potential sources of lead in their patients’ lives in order to prevent health effects. As stated in the article, the typical method of determining lead exposure is to measure blood lead levels. This is often thought to be far from ideal owing to the short half-life of lead in blood, which is certainly true in adults for whom values of half-life are cited at 15 days.² However, Manton et al³ put forward evidence based on lead isotope ratio analysis that the half-life of lead in the blood of young children can range from 20 to 38 months for prolonged exposure and from 8 to 11 months for a brief exposure. With this in mind, for children younger than 2 years of age, it might be that blood lead is as valid as any other indicator of cumulative lead exposure.

For adults, bone lead measured noninvasively by K x-ray fluorescence has been shown to reflect long-term cumulative exposure to lead⁴; this might also be the case for older children, but it has not been explicitly demonstrated. Bone lead measurements have previously been conducted in children between the ages of 6 and 19 years from Hamilton, Ont.⁵ Also, as reported at the recent Lead International Strategic Opportunities Program workshop—held in June 2010 at McMaster University in Hamilton—Health Canada, in collaboration with McMaster University and St Joseph’s Health Centre in Toronto, Ont, is currently performing a study in which participants as young as 1 year of age are actively being recruited for bone and blood lead measurements. We encourage physicians to find more information about this continuing study on the Health Canada website.⁶ Bone measurements have also been conducted in children using the alternative L x-ray fluorescence technique,⁷ but this method is particularly sensitive to slight movements and so is thought by some to be difficult to use in practice.

Bone lead measurement by x-ray fluorescence is non-invasive, and thousands of measurements, mostly on adults, have been made worldwide. McMaster University offers this service to Ontario physicians through Hamilton Health Sciences. Thus, we encourage those seeking more diagnostic information on lead-exposed subjects (of any age older than 1 year) to consider bone lead as a practical means of determining the lead body burden. None of the foregoing should be allowed to detract from the value and importance of the practical advice, particularly with the emphasis on prevention, offered by Abelsohn and Sanborn.¹