Tuesday, August 28, 2012

Lead testing

Lead is a bad thing to ingest. How bad? Don’t worry about it.

Lead is a good thing to test. When? Don’t worry about it. How? Don’t worry about it.

I find lack of information leads to more worrying than an abundance of information, so here’s what I’ve learned:

The CDC used to tell everyone not to worry about blood lead levels less than 10 µg/dl in children up to age 6, but recently lowered that to less than 5 µg/dl. So if it’s less than 5, everything is fine.

Unless you believe the studies which all agree that there is no safe level. There was nothing magical about 10, and there’s nothing magical about 5. There are just cost/benefit analyses. A few µg higher will cost you a few IQ points permanently, but you probably weren’t going to use all those IQ points anyway. The lower the lead level, the more IQ points each µg costs you.

What can you do to reduce blood lead levels? Reduce exposure. Chelation is not recommended for moderate amounts of lead.

Blood lead testing only measures exposure over the past month or two. It’s not the same as measuring uptake into various tissues.

EP or ZPP testing can give some additional info:

The EP helps to determine whether the lead in the child's system is having any type of effect on the body that we can measure. EP is one of the only ways to look for an effect of lead on the child. By looking at EP we can get a better idea of how much lead is in the body. Another way to think about EP is this: because EP is made in the body’s tissues, if EP is elevated, it suggests that other body tissues (such as the kidney or brain) are also being affected by the lead.

The EP can sometimes also be used to determine for how long the child was exposed to lead. It can also determine whether the child is still being exposed to lead; when children have another exposure to lead, the EP will rise. Finally, the EP helps the doctor to manage the child’s lead poisoning; as the lead poisoning is treated (for example, with chelation), the EP falls to the normal range.
Back to blood lead level testing. There are different testing methods, and the results are not always consistent. They have varying degrees of accuracy, varying lower threshholds, and may consistently underestimate or overestimate the amount of lead in the sample.

Winchester Hospital reports out any result less than 1.4 as simply less than 1.4. Boston Children’s Hospital uses GFAAS and reports out any result less than 2 as simply less than 2. Quest reports out any result less than 3.3 or 3.5 as simply less than 3.3 or 3.5 (according to our pediatrician).

I’d love to find a local lab that uses ICP-MS, which can be reasonably accurate down to 0.1, but no luck yet.

Some sources: www.who.int/ipcs/assessment/public_health/lead_blood.pdf, www.clevelandcliniclabs.com/portals/66/PDF/TechBriefs/LeadTechBrief.pdf, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2212280/, http://www.childrenshospital.org/clinicalservices/Site1899/mainpageS1899P7.html, http://www.childrenshospital.org/clinicalservices/Site1899/mainpageS1899P6.html, calls to Boston Children’s Hospital Chemistry Lab (don’t bother with Lab Control, Drawing Lab, or the Blood Donor Center).

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