Coproporphyrin III is a derivative of porphyrin.

Coproporphyrin III methyl ester is repeatedly isolated in a considerable amount from both feces and urine. A great increase of coproporphyrin III excretion is unaccompanied by symptoms or signs of porphyria, metal, or chemical poisoning or liver disease [1]. In the presence of the porphyrin precursor, 5-aminolevulinate (ALA), the addition of insulin causes a striking increase in the accumulation of uroporphyrin I and coproporphyrin III. Antioxidants abolish the uroporphyrin I accumulation and increases coproporphyrin III [2].

Urinary porphyrin and DMA profile can be used as an early warning biomarker for chronic MMA exposure before the onset of cancer. After 4 weeks the level of coproporphyrin III concentration significantly increases in all the treatment groups compared to the control [3].