Lead accumulates slowly in the body and even low doses can eventually lead to poisoning. Serum level of lead at which treatment is indicated in young children is 100mcg/l. 95% of lead in body is deposited in bones and teeth while 99% of lead in blood is associated with erythrocytes. Lead poisoning can cause nervous system toxicity and renal tubular dysfunction leading to irreversible interstitial nephrosis with progressive renal impairment and hypertension. Lead also depresses haem synthesis and shortens life span of erythrocytes causing a hypochromic microcytic anaemia.
Incidence A lot less common than it used to be with less use in petrol, paints or cosmetics and generally improved housing.
Symptoms Mild poisoning - lethargy with occasional abdominal discomfort. 2
Severe poisoning - usually diffuse abdominal pain but may be colicky, vomiting, constipation and encephalopathy. Latter is more common in children with seizures, mania, delirium and coma. Foot drop due to motor peripheral neuropathy is a classic sign. Wrist drop is a late sign.
Headaches, hearing loss, carpal tunnel syndrome and sub-fertility can also occur.
Signs May see blue discoloration of gum margins.
Investigations Serum lead levels (normal <100mcg/l), blood film (basophilic stippling of erythrocytes), FBC, X-ray fluorescence to estimate total body burden. Lead lines may be visible in growing bones.
Toxic Blood Levels
<100mcg/l - Normal.
>100mcg/l - May cause impaired cognitive development in children.
>450mcg/l - GI symptoms in adults and children. Oral chelation therapy should commence.
>700mcg/l - High risk of acute CNS symptoms. Parenteral chelation treatment should be commenced.
>1000mcg/l - may be life threatening.
Drugs In severe poisoning with encepalopathy: Dimercaprol (BAL) and calcium disodium edetate (given parenterally), or if less severe and no encephalopathy: DMSA (Succimer) can be given by mouth. Penicillamine has also been used for decades as an unlicensed oral alternative.
Note that if chelation therapy is ceased prematurely the blood levels can rebound due to movement of the metal out of the bony stores.
Prevention Stopping working with lead at serum > 600-700mcg/l.
Acknowledgements EMIS is grateful to doctoronline.nhs.uk for facilitating draft authoring of this article. The final copy has passed peer review of the independent Mentor GP authoring team. ?EMIS 2004.