What is being tested?
The zinc protoporphyrin (ZPP) test is a blood test that can identify a disruption in the formation of heme. Heme is an essential component of hemoglobin, the protein in red blood cells (RBCs) that carries oxygen from the lungs to the body’s tissues and cells. The formation of heme occurs in a series of enzymatic steps that conclude with the insertion of an iron atom into the center of a molecule called protoporphyrin. If there is not enough iron available, then protoporphyrin combines with zinc instead of iron to form zinc protoporphyrin. Since it cannot transport oxygen, ZPP serves no useful purpose in the RBCs that contain it.

ZPP is measured in 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 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 your 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.

Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.