Acute Intermittent Porphyria (AIP) Hereditary Coproporphyria (HCP) PBG (Porphobilinogen) Variegate Porphyria (VP)
Porphobilinogen Qnt, U (PBGU)
First-order test for evaluation of a suspected acute porphyria: acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria
1. Collect a random urine specimen.
2. No preservative necessary but pH must be >5.0.
3. Specimens should be frozen immediately following collection.
**Ship specimen protected from light.**
It is recommended that specimen collection occur during the acute phase. Porphobilinogen (PBG) may be normal when the patient is not exhibiting symptoms.
If the specimen is collected after treatment is initiated, the level of PBG excreted may be decreased.
Specimens should be frozen immediately following collection and protected from light. PBG is susceptible to degradation at high temperatures, at pH below 5.0, and on prolonged exposure to light.
The porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Depending on the specific enzyme involved, various porphyrins and their precursors accumulate in different specimen types. The patterns of porphyrin accumulation in erythrocytes and plasma and excretion of the heme precursors in urine and feces allow for the detection and differentiation of the porphyrias.
The porphyrias are typically classified as erythropoietic or hepatic based upon the primary site of the enzyme defect. In addition, hepatic porphyrias can be further classified as chronic or acute, based on their clinical presentation.
The primary acute hepatic porphyrias: acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP), are associated with neurovisceral symptoms that typically onset during puberty or later. Common symptoms include severe abdominal pain, peripheral neuropathy, and psychiatric symptoms. A broad range of medications (including barbiturates and sulfa drugs), alcohol, infection, starvation, heavy metals, and hormonal changes may precipitate crises. Photosensitivity is not associated with AIP but may be present in HCP and VP.
Urinary porphobilinogen (PBG) is elevated during the acute phase of the neurologic porphyrias. Urine and fecal porphyrin analysis should be performed to confirm the diagnosis and to distinguish between AIP, HCP and VP. A biochemical diagnosis of AIP can be confirmed by measurement of PBG deaminase activity using PBGD_ / Porphobilinogen Deaminase, Whole Blood. VP and HCP can be confirmed by measurement of fecal porphyrins (FQPPS / Porphyrins, Feces). Once the biochemical diagnosis of an acute porphyria is established, molecular genetic testing is available, which allows for diagnosis of at-risk family members.
The workup of patients with a suspected porphyria is most effective when following a stepwise approach. The following algorithms are available in Special Instructions or call 800-533-1710 to discuss testing strategies.
Abnormal results are reported with a detailed interpretation that may include an overview of the results and their significance, a correlation to available clinical information provided with the specimen, differential diagnosis, and recommendations for additional testing when indicated and available, and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.