Zinc Protoporphyrin

Other names: Free Erythrocyte Protoporphyrin; ZPP; FEP; ZP

The zinc protoporphyrin test is used to detect a disruption in the production of haem; haem is a component part of haemoglobin, the protein in red blood cells, which is responsible for carrying oxygen around the body. Haem is formed by a series of enzymatic processes; the last step is the insertion of an atom of iron into the middle of a molecule known as protoporphyrin. If an individual does not have sufficient iron supplies, zinc will be used instead and the zinc will combine with protoporphyrin. Zinc protoporphyrin cannot carry oxygen so it is not a useful component of red blood cells.

When is the test used?

The test is used to detect overexposure to lead; it may also be used to test for iron deficiency in children.

The test is usually ordered for people who are exposed to lead on a regular basis (usually as part of their job) or when a patient has symptoms of lead poisoning. The test may be ordered when a child shows possible symptoms of iron deficiency but this is not common.

How is the test done?

ZPP is measured in two different ways; the free erythrocyte protoporphyrin (FEP) test measures the concentration of free protoporphyrin and this result can be used to determine the ZPP/haem ratio. The FEP test is done by taking a sample of blood from a vein in the patient’s arm; a needle is inserted into the vein and the blood is collected in a syringe. The ZPP/haem ratio is worked out by collecting a sample of blood from the finger tip and using a machine called a haematoflurometer.

What do the test results show?

The concentration of ZPP in the blood is usually very low; if levels are higher than usual this indicates that there is a disruption in the production of haem. The test cannot determine the cause of the disruption but the most common causes are lead poisoning and iron deficiency. Other tests results will always be considered alongside the results of the ZPP test.

Health conditions, including inflammation, infections and blood-related disease may also affect ZPP levels.

Specific Blood Tests

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