Lead mining in Southern Scotland. The beam engine at the former lead mine in Wanlockhead, c. 1900. This now forms part of the Lead Mining Museum. Photograph courtesy of the Wanlockhead Museum Trust.
Inorganic lead compounds have been known to be a toxic hazard for many hundreds of years. Control of lead exposure at work is covered by regulations (Control of Lead at Work, or CLAW)38 which stipulate regular blood lead monitoring. Environmental exposure to lead has reduced considerably with the introduction of lead-free petrol, removal of lead from paint, reduction of lead in potable water supplies, removal of lead plumbing, and treatment of water to reduce plumbo-solvency. Nevertheless, lead poisoning can still occur, usually as a result of occupational exposure, in plumbers, stain glass window workers, paint strippers etc.
Blood lead measurement provides a reliable guide to lead exposure. The industrial action limit, above which workers are legally required to be suspended from work, is currently 2.90 µmol/L (60 µg/100 mL).39 Lead inhibits several enzymes in the haem cycle and so concentrations of several porphyrins increase especially when blood lead exceeds 2.0 µmol/L. At about this concentration other effects may result such as fatigue, depression, irritability, cognitive impairment, headaches, weakness and constipation. More severe poisoning may cause anaemia, renal tubular dysfunction and peripheral neuropathy. Zinc protoporphyrin (ZPP) can be measured as an alternative marker although this analyte also increases in patients with iron deficiency anaemia.
In children, lead may have significant neurological effects. Children are more prone to exposure since intestinal absorption is more efficient than in adults. Pica, the repetitive ingestion of non-food substances by young children, may present a hazard in poorly maintained housing with lead-based paint. The traditional remedies of a number of non-Western areas of the world may contain substantial amounts of lead and several instances of clinical lead poisoning by ingestion of Asian traditional remedies have been reported in the UK. Middle Eastern and Asian eye cosmetics may also contain lead, and their use on infants or by their mothers is associated with increased blood lead levels in the infants concerned. Ingestion of traditional remedies or application of eye cosmetics is now the commonest form of lead poisoning in children.
Subtle toxic effects of lead on behaviour can be found even in children whose blood lead concentrations are ‘normal’.40 In 2012 the US Center for Disease Control (CDC) reduced the reference threshold concentration for lead in children under five years to ≤ 0.24 µmol/L.41 This follows results from the most recent population survey of blood lead concentrations in the United States which showed that the 97.5th percentile is at 5 µg/dL (0.24 µmol/L) and this is now the CDC upper reference value, replacing the previous 10 µg/dL ‘level of concern’.42
The measurement of urinary lead is only recommended for monitoring of chelation therapy or for assessment of exposure to alkyl-leads.
Sample Requirements and Reference Ranges for Lead
|Sample Type||Blood*, water**|
Blood: EDTA or lithium heparin (non-gel).
Water: Universal container
|Precautions||Blood samples for occupational exposure should be taken at the end of a working shift. Contamination is associated with some paediatric containers and with some containers with rubber inserts or O-rings in the cap. These samples and lithium heparin gel tubes are unsuitable.|
Blood: 350 µL***
Water: 1 mL
Blood lead: < 0.24 µmol/L (5 µg/100mL): age ≤ 5 years41
< 0.48 µmol/L (10 µg/100mL): age > 5 years
> 2.90 µmol/L (60 µg/100mL) (CLAW suspension limit)38
ZPP: 30 to 80 µmol/mol haemoglobin
Water: < 10 µg/L (Current EU limit for drinking water)
Blood: 3.5 days (please telephone 0141 211 5178 if urgent result is required)
|Method||Inductively coupled plasma mass spectrometry|
Blood: Traceable to reference material produced in accordance with EN ISO 17511:2003 “In vitro diagnostic medical devices. Measurement of quantities in biological samples. Metrological traceability of values assigned to calibrators and control materials” and reference materials with values determined by reference laboratories.
Water: Traceable to certified reference material ERM CA022a
|Intermediate Precision (CV)||Blood: 12.1% at 0.05 µmol/L, 3.5% at 2.48 µmol/L|
|Measurement Uncertainty, U||Blood: 0.05 ± 0.01 µmol/L, 2.48 ± 0.18 µmol/L|
|Analytical Goals (CV)||Blood: Acceptable: 9.5%, Desirable: 6.3%****|
|EQA Scheme||Blood: UK NEQAS, Guildford and UK NEQAS Cd and Pb, Birmingham.|
* One sample of blood is sufficient for blood lead and ZPP analysis.
** For assessment of lead in water, two samples are recommended; a first draw sample in the morning and a further sample taken after running the water for 5 - 10 mins.
*** Absolute minimum volume; this volume is insufficient to carry out repeat analysis if analysis fails.
**** Goal origin: biological variation43