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Trace
Elements Laboratory |
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A
Joint Venture of London Health Sciences Centre and St. Joseph's
Health Care London
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Zinc Protoporphyrin (ZPP)
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| Atomic
Number: |
30 |
| Atomic
Symbol: |
Zn |
| Atomic
Weight: |
65.38 |
| Electron
Configuration: |
[Ar]4s23d10 |
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| TITLE |
Zinc
Protoporphyrin (ZPP) |
| GENERAL
INFORMATION |
Heme
is synthesized in the erythrocyte through a series
of reactions. In the last reaction, Ferrochelatase
catalyzes the incorporation of Fe2+ into protoporphyrin
molecule to form heme. When the enzyme activity is
inhibited by lead or iron supply is insufficient,
Fe2+ cannot be inserted into protoporphyrin. Consequently,
Zn2+ takes the place of Fe2+ to be inserted into protoporphyrin
nonenzymatically to yield ZPP. Once formed, ZPP is
stable and remains bound in erythrocytes during their
120-day life span (2). ZPP levels rise and decline
to baseline more slowly than blood lead levels, a
ZPP determination along with the blood lead testing
can help differentiate acute from chronic exposure.
However, the ZPP test has its disadvantages in monitoring
lead toxicity. It is not sufficiently sensitive for
low level lead exposure. In 1991, the CDC defined
lead poisoning in children as a blood lead level of
0.48 µmol/L (100 µg/L) (3). At this blood
lead level, ZPP has poor diagnostic sensitivity, so
it should not be used as a screening test for lead
poisoning in children. In addition, ZPP is not specific
for lead exposure because it may also be elevated
in iron deficiency anemia.
The ZPP level is determined by a ProtoFluor-Z Hematofluorometer.
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MONITORING/CLINICAL
INTERPRETATION
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Elevated
ZPP levels may indicate long-term lead exposure or
iron deficiency anemia.
An increase
in the concentration of ZPP may occur at blood lead
levels of 200-300 µg/L. Increases in ZPP become
more significant once the blood lead level has reached
400 µg/L. Increases in blood lead levels beyond
400 µg/100 g are associated with exponential
increases in ZPP (4).
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| MATRIX
CHOICE |
Whole
blood |
| REFERENCES |
1.
National Committee on Clinical Laboratory Standards.
C42-P. Erythrocyte protoporphyrin testing: approved
guideline. Villanova, PA: NCCLS, 1996
2. Stanton NV, et al: Empirically determined lead-poisoning
screening cutoff for the Protofluor-Z hematofluorometer.
Clin Chem 1989;35(10):2104-2107
3. Centers of disease control. Preventing lead poisoning
in young children. A statement of the centers for
disease control. Atlanta: CDC, 1991.
4. OSHA Medical Surveillance Guidelines: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10644
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TEST
INFORMATION/
REFERENCE RANGES
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