Porphobilinogen !

Porphobilinogen is the first pyrrole ring of heme synthesis; high in urine, it points to an acute porphyria attack.

Updated 2026-11-01

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Key facts

It is made from two ALA (ALA dehydratase), and four of them form hydroxymethylbilane (PBG deaminase).
It is colourless, but in urine exposed to light and air it polymerises to porphobilin, red-brown in colour.
Very high urine porphobilinogen: the test of choice when an attack of acute intermittent porphyria, coproporphyria or variegate porphyria is suspected.
It is normal in lead poisoning and ALA dehydratase deficiency, where only ALA rises.

A single pyrrole with an acetate chain, a propionate chain and an aminomethyl group, lost as NH₃ when it links to the others.

The sample is protected from light; the result is expressed per gram of creatinine in a spot urine, so diagnosis is not delayed.
Between attacks it may stay high in acute intermittent porphyria but fall to normal in coproporphyria and variegate porphyria.
The classic qualitative test uses Ehrlich's reagent; today quantitative measurement is preferred.

Think of the answer, then tap the question to see it.

Which test confirms an acute porphyria attack?

Markedly raised urine porphobilinogen, measured in a light-protected spot sample.

Why does urine from a porphyria attack darken on standing?

Colourless porphobilinogen polymerises to red-brown porphobilin with light and air.

What is porphobilinogen like in lead poisoning?

Normal: lead blocks ALA dehydratase, before porphobilinogen is formed.

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Porphobilinogen (CID 1021) (PubChem, NCBI, 2026) · Public domain; Porphyrins urine test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Porphyria: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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