Protoporphyrin IX Unit Converter

Protoporphyrin IX (PPIX) is the immediate precursor to heme, the iron-containing molecule that allows red blood cells to carry oxygen. In the final step of heme production, the enzyme ferrochelatase inserts iron into protoporphyrin IX to form functional heme.

When this conversion is disrupted, whether by iron deficiency, lead exposure, or an inherited enzyme defect, free (metal-free) protoporphyrin IX accumulates in red blood cells. This test measures the level of that unconverted protoporphyrin.

In healthy individuals, nearly all erythrocyte protoporphyrin exists as zinc protoporphyrin rather than free protoporphyrin IX. A predominance of the metal-free form is a hallmark of erythropoietic protoporphyria.

Protoporphyrin IX is produced in the mitochondria of developing red blood cells in the bone marrow and, to a lesser extent, in liver cells. It is the final intermediate of the eight-step heme biosynthesis pathway, formed when protoporphyrinogen IX is oxidized by the enzyme protoporphyrinogen oxidase.