Zinc Protoporphyrin (ZPP)

The ZPP concentration in blood is usually very low. An increase in ZPP indicates a disruption of normal heme production but is not specific as to its cause. The main reasons for increases in ZPP are iron deficiency and lead poisoning. It is important that ZPP concentrations be evaluated in the context of a patient’s history, clinical findings, and the results of other tests such as ferritin, lead, and a complete blood count (CBC). It is possible that the patient may have both iron deficiency and lead poisoning.

In cases of chronic lead exposure, ZPP reflects the average lead concentration over the previous 3-4 months. However, the amount of lead currently present in the blood and the burden of lead in the body (the amount in the organs and bones) cannot be determined with a ZPP test. Values for ZPP rise more slowly than the blood lead concentration following exposure, and they take longer to drop after exposure to lead has ceased.

ZPP levels must be evaluated in the context of your history, clinical findings, and the results of other tests such as ferritin, lead, and a complete blood count (CBC). You may have both iron deficiency and lead poisoning.

In cases of chronic lead exposure, ZPP reflects the average lead level over the previous three to four months. However, the amount of lead currently present in the blood and the amount in the organs and bones cannot be determined with a ZPP test. Values for ZPP rise more slowly than blood lead concentrations following exposure and take longer to drop after exposure to lead has ceased.

ZPP can also be elevated in anemia caused by chronic inflammatory diseases, infections, and cancer, but it is not generally used to monitor or diagnose these diseases.

Depending on the method used to test ZPP, high levels of other substances in the blood, such as bilirubin and riboflavin, can produce false-positive results. Falsely low values may occur if the sample is not protected from light before testing.

What is Zinc protoporphyrin (ZPP)?

Zinc protoporphyrin (ZPP) is a normal metabolite that accumulates in trace amounts in erythrocytes (Red blood cells) during hemoglobin (=a protein in red blood cells that carries oxygen) synthesis (=the production of hemoglobin). 

The final step in the heme pathway involves the enzyme ferrochelatase, which binds ferrous iron with protoporphyrin IX through a process called chelation. This reaction is crucial for the synthesis of heme, a compound that plays a vital role in various biological functions such as oxygen transport. However, in cases of iron deficiency or impaired iron utilization, an alternative metal substrate, zinc, can be used by ferrochelatase. On the other hand, lead toxicity can interfere with the transfer of iron within cells, leading to a condition similar to iron deficiency. Essentially, lead toxicity mimics the effects of iron deficiency by disrupting the normal functioning of intracellular iron transfer.