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LEADO
300115
recognized as a risk factor for atherosclerotic disease, specifically coronary atherosclerosis. Diminished or
absent (abetalipoproteinemia) LDLC may be a cause of polyneuropathy.
Useful For: Evaluation of cardiovascular risks Diagnosis of hypobetalipoproteinemia, if appropriate
clinical information is provided Diagnosis of abetalipoproteinemia
Interpretation: Evaluation of cardiovascular risk is based on the following range of values established
by the National Cholesterol Education Program (NCEP): -Desirable:
or =190 mg/dL Decreased values may indicate hypobetalipoproteinemia. Nondetectable low density
lipoprotein cholesterol indicates abetalipoproteinemia. Related polyneuropathy may exist in affected
individuals.
Reference Values:
The National Cholesterol Education Program (NCEP) has set the following guidelines (reference values)
for LDLC:
Optimal: or =190 mg/dL
Clinical References: Executive Summary of the Third Report of the National Cholesterol Education
Program (NCEP) Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in
Adults (Adult Treatment Panel III), JAMA 2001;285:2486-2497
Lead Profile Occupational Exposure, Blood
Clinical Information: Lead is a heavy metal commonly found in the man's environment that can be
an acute and chronic toxin. Lead is present in paints manufactured before 1970. It was banned from
household paints in 1972 but is still found in paint produced for nondomestic use and in artistic pigments.
Ceramic products available from noncommercial suppliers (such as local artists) often contain significant
amounts of lead that can be leached from the ceramic by weak acids such as vinegar and fruit juices. Lead
is found in dirt from areas adjacent to homes painted with lead-based paints and highways where lead
accumulates from use of leaded gasoline. Use of leaded gasoline has diminished significantly since the
introduction of unleaded gasoline, which has been required in personal automobiles since 1972. Lead is
found in soil near abandoned industrial sites where lead may have been used. Water transported through
lead or lead-soldered pipe will contain some lead with higher concentrations found in water that is weakly
acidic. Some foods (eg, moonshine distilled in lead pipes) and some traditional home medicines contain
lead. Exposure to lead from any of these sources either by ingestion, inhalation, or dermal contact can
cause significant toxicity. Lead expresses its toxicity by several mechanisms. It avidly inhibits
aminolevulinic acid dehydratase (ALA-D) and ferrochelatase, 2 of the enzymes that catalyze synthesis of
heme. Inhibition of ALA-D and ferrochelatase causes accumulation of delta aminolevulinic acid in urine
and protoporphyrin in erythrocytes, which are markers for significant lead exposure. Lead also is an
electrophile that avidly forms covalent bonds with the sulfhydryl group of cysteine in proteins. Thus,
proteins in any tissues exposed to lead will have lead bound to them. Keratin in hair contains a high
fraction of cysteine relative to other amino acids. The cysteine residues are cross-linked through lead,
thereby causing the tertiary structure of the protein to change; cells of the nervous system are particularly
susceptible to this effect. Some lead-bound proteins change their tertiary configuration sufficiently that
they become antigenic; renal tubular cells are particularly susceptible to this effect because they are
exposed to relatively high lead concentrations during clearance. A typical diet in the United States
contributes approximately 300 mcg of lead per day, of which 1% to 10% is absorbed; children may absorb
as much as 50% of the dietary intake, and the fraction of lead absorbed is enhanced by nutritional
deficiency. The majority of the daily intake is excreted in the stool after direct passage through the
gastrointestinal tract. While a significant fraction of the absorbed lead is rapidly incorporated into bone
and erythrocytes, lead ultimately distributes among all tissues, with lipid-dense tissues such as the central
nervous system being particularly sensitive to organic forms of lead. All lead absorbed is ultimately
excreted in the bile or urine. Soft-tissue turnover of lead occurs within approximately 120 days.
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