Porphobilinogen (PBG)

Porphobilinogen (PBG) is an intermediate in heme synthesis produced from delta‑aminolevulinic acid (ALA). In acute hepatic porphyrias, enzyme defects cause PBG to accumulate and be excreted in urine during neurovisceral attacks. A markedly raised urine PBG level is a key diagnostic marker for acute porphyria and helps distinguish attacks from other causes of abdominal pain and neuropathy.

Elevated porphobilinogen (PBG) in urine indicates an acute hepatic porphyria, most commonly acute intermittent porphyria. It reflects defective heme synthesis with accumulation of neurotoxic intermediates, often during acute attacks presenting with severe abdominal pain, neuropathy, and psychiatric symptoms. Increased urinary PBG requires urgent clinical evaluation, repeat testing during symptoms, and genetic or enzymatic confirmation for diagnosis and management.

Normal urinary porphobilinogen (PBG) is very low—generally under about 2–4 mg per 24 hours (commonly cited as <3 mg/24 h). Values above this range, particularly markedly raised levels, suggest an acute porphyria and need prompt clinical evaluation and confirmatory testing. Lab units and reference intervals vary, so always review the specific lab’s range with your clinician.

Increased urinary porphobilinogen (PBG) is seen in the acute hepatic porphyrias — most characteristically acute intermittent porphyria (AIP) during attacks. Elevated PBG also occurs in other acute porphyrias such as hereditary coproporphyria, variegate porphyria and the rare ALA‑dehydratase (ALAD) deficiency porphyria. Testing is most reliable on urine collected during an acute neurovisceral attack.

PBG stands for postprandial blood glucose — the blood sugar level measured after eating, typically one to two hours post-meal. It helps assess how well the body handles glucose and guides diabetes management. Normal postprandial targets are usually below about 140 mg/dL for non‑diabetic people, while targets for people with diabetes are individualized based on clinical advice.

Porphyria is a group of inherited metabolic disorders affecting heme synthesis. It is not a primary mental illness, but some types — especially acute hepatic porphyrias — can produce neurological and psychiatric symptoms (anxiety, confusion, hallucinations, depression) during attacks. These psychiatric features reflect the underlying metabolic disease and require medical evaluation and treatment of porphyria alongside supportive mental-health care.