Clinical Pathology: Clinical Chemistry

• Lead intoxications can be either chronic or acute. Acute intoxications can lead to gastrointestinal and renal symptoms. In addition to these symptoms, chronic intoxications have cardiovascular, endocrine, developmental, and neurologic effects.

• In blood, 99% of lead is bound to erythrocytes, which is one of the reasons lead levels are measured in whole blood samples. The bioavailability of lead after oral administration is approximately 20%. Lead is distributed in blood (2%), soft tissue (3%), and mineralized tissue, such as bone (95%), where it is sequestered and then slowly released. The elimination of lead is multiphasic, with half-lives of 36 days and 4 years.

• Blood collection tubes containing EDTA should not be used for whole blood assays because EDTA can chelate lead and cause low readings when a flame atomic absorption spectrometry method is used.

• The most common methods used to measure lead are flame atomic absorption spectrometry (AAS), graphite furnace atomic absorption spectrometry (GFAAS), anode stripping voltammetry (ASV), inductively coupled plasma–atomic emission spectroscopy (ICP-AES), and inductively coupled plasma mass spectrometry (ICP-MS)

• Normal ranges for blood lead are less than 100 to 200 ng/mL. In this clinical case, a potentially increasing, already elevated, blood lead level indicates that chelation therapy is necessary, despite the absence of symptoms. In this patient, a second lead level measured in a sample collected 9.5 hours after the acute intoxication was 412.9 ng/mL, confirming that the initiation of chelation therapy was the correct approach.

• Several intravenous and oral chelators are available, such as dimercaptopropane sulfonate sodium, EDTA, and succimer.

• Several markers of the effects of lead can also be determined to support blood lead measurements. These include measuring δ-aminolevulinic acid (ALA) excretion and δ-aminolevulinic acid dehydratase (ALA-D) enzymatic activity.

Ho G, Keutgens A, Schoofs R, et al: Blood, urine, and hair analysis following an acute lead intoxication. J Anal Toxicol 2011;35:60–64.

Graziano JH: Validity of lead exposure markers in diagnosis and surveillance. Clin Chem 1994;40:1387–1390.

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