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Zinc Protoporphyrin

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Also known as: ZPP; ZP; Free Erythrocyte Protoporphyrin; FEP; ZPP/Heme Ratio
Formal name: Zinc Protoporphyrin

At a Glance

Why Get Tested?

To screen for and monitor chronic exposure to lead in adults; to detect iron deficiency in children

When to Get Tested?

When you have been chronically exposed to lead, as part of a program to monitor lead exposure, and/or when your healthcare provider suspects lead poisoning; as part of a screening program for iron deficiency in children and adolescents

Sample Required?

A blood sample drawn from a vein in your arm or from a fingerstick

Test Preparation Needed?

None

The Test Sample

What is being tested?

Zinc protoporphyrin (ZPP) is normally present in red blood cells in small amounts, but the level may increase in people with lead poisoning and iron deficiency. This test measures the level of ZPP in the blood.

To understand how lead poisoning and iron deficiency affect the ZPP level, it is first necessary to know about heme. Heme is an essential component of hemoglobin, the protein in red blood cells that carries oxygen from the lungs to the body's tissues and cells.

The formation of heme occurs in a series of steps that conclude with the insertion of an iron atom into the center of a molecule called protoporphyrin. When there is not enough iron available, as in iron deficiency, or when the insertion of iron is inhibited, as in lead poisoning, then protoporphyrin combines with zinc instead of iron to form zinc protoporphyrin. ZPP serves no useful purpose in red blood cells since it cannot bind to oxygen.

ZPP may be measured in one of two ways:

  • The free erythrocyte protoporphyrin (FEP) test measures both ZPP, which accounts for 90% of protoporphyrin in red blood cells, and free protoporphyrin, which is not bound to zinc.
  • The ZPP/heme ratio gives the proportion of ZPP compared to the normal iron-containing heme in red blood cells.

How is the sample collected for testing?

To measure FEP, a blood sample is taken by inserting a needle into a vein in the arm. To determine the ZPP/heme ratio, a drop of blood from a fingerstick is placed in an instrument called a hematofluorometer. This instrument measures the fluorescence of ZPP and reports the amount of ZPP per number of heme molecules. Since only a single drop of blood is required, this test is well suited for screening children.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

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Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pg 1056.

Magge H, et al. Zinc Protoporphyrin and Iron Deficiency ScreeningTrends and Therapeutic Response in an Urban Pediatric Center. JAMA Pediatr. 2013;167(4):361-367. Available online at http://archpedi.jamanetwork.com/article.aspx?articleid=1653081 through http://archpedi.jamanetwork.com. Accessed August 2014.

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