Porphyrins, Quantitative, 24 Hr Urine

Overview:

Evaluate porphyrias, including those involving deficiencies of enzymes that are needed for heme synthesis and chemical porphyrias.

In congenital erythropoietic porphyria, elevations of urinary uroporphyrin and coproporphyrin occur, with the former exceeding the latter.

In acute intermittent porphyria, porphobilinogen and δ-aminolevulinic acid are elevated in acute attacks, and mild increases of urinary uroporphyrin and coproporphyrin may be found. Porphobilinogen is increased in many but not all patients with acute intermittent porphyria in latent periods. Quantitative porphobilinogen is a better test than δ-aminolevulinic acid overall for acute intermittent porphyria, but both are used (as well as the Watson-Schwartz test).¹

Coproporphyrin and porphobilinogen excretion in urine are markedly increased during acute attacks of hereditary coproporphyria, increase of urinary uroporphyrin may be found, and increased fecal coproporphyrin III is described.

In variegate porphyria in acute attacks, results are similar to those of acute intermittent porphyria. Porphobilinogen and ALA are prone to become normal between attacks. Urine coproporphyrin exceeds uroporphyrin excretion during acute attacks.

Chemical porphyrias occur. Porphyrinogenic chemicals include certain halogenated hydrocarbons that cause the excretion of increased uroporphyrin.

In lead poisoning elevation of δ-aminolevulinic acid greater than that of porphobilinogen occurs and porphobilinogen may be normal. Urinary coproporphyrin characteristically is increased. Free erythrocyte protoporphyrin is increased. Toxins such as lead interfere with heme synthesis and cause porphyrinuria.

Increased urine excretion of uroporphyrinogen, uroporphyrin, and coproporphyrin occurs in porphyria cutanea tarda. It is found in (1) middle-aged men who like ethanol, (2) young women on oral contraceptives, and in (3) subjects on dialysis. These patients do not excrete increased porphobilinogen, but they may have slight elevations of δ-aminolevulinic acid.

Increased urine porphyrin excretion may be secondary to other diseases (eg, hepatobiliary diseases), especially coproporphyrin excretion. These are secondary porphyrinurias. They lack increased urinary porphobilinogen or Δ-ALA, with the important exception of lead poisoning.² The table provides an abbreviated overview of the porphyrias. Porphyrin fractionation of plasma can be done. Increases of urine porphyrins are found with congenital erythropoietic porphyria, acute intermittent porphyria, hereditary coproporphyria, variegate porphyria, and porphyria cutanea tarda.

Fecal porphyrin examination for hereditary coproporphyria, variegate porphyria, and protoporphyria can be used for adult patients. Stool examination for coproporphyrin and protoporphyrin is recommended for diagnosis of variegate porphyria.³

Neurologic dysfunction occurs in the hepatic porphyrias, the types of porphyria in which acute attacks develop: acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and ALA dehydrase deficiency. Abdominal pain, caused by autonomic neuropathy, occurs with acute attacks (eg, acute intermittent porphyria). It is the most common symptom of acute intermittent porphyria.²

Cutaneous aspects of the porphyrias are caused by photosensitization (eg, porphyria cutanea tarda, protoporphyria).

Hepatic complications are found with porphyria cutanea tarda and protoporphyria. Fluorescence is demonstrable in liver biopsies from patients with the former, as well as siderosis. Crystalline deposits may be found in protoporphyria.² The amount of porphobilinogen excreted in acute intermittent porphyria is usually greater than the excretion of δ-aminolevulinic acid (Δ-ALA). When there is more Δ-ALA, another diagnosis should be considered, including lead poisoning, another type of porphyria, or hereditary tyrosinemia.² See also Zinc Protoporphyrin (ZPP) [010170], which pertains to lead poisoning, and erythropoietic protoporphyria. The differential diagnosis of lead poisoning is relevant.⁴