Diagnostic and intervention algorithm for patients presenting with signs and symptoms suspicious for an AHP attack. The neurovisceral manifestations of an attack with AIP are similar to those with HCP and VP. HCP and VP may also have a history of blistering skin rash on sun-exposed areas. A rapid spot urine quantitative assay for PBG can identify pathological accumulation and hyperexcretion of PBG and, by inference, ALA, the neurotoxic precursors that cause acute signs and symptoms. A urine PBG/creatinine ratio >10 mg/g is a sensitive and specific indicator of an AHP. Importantly, asymptomatic patients with AHP (particularly AIP) can have basal high urine PBG levels; therefore, it is always important to evaluate for alternative etiologies and porphyrinogenic triggers of acute signs and symptoms (eg, infection). Additional studies of urine, stool, and blood are needed to fully characterize the AHP subtype biochemically. Genetic testing is not appropriate for initial screening but is used to confirm the diagnosis based on biochemical testing results and can be very helpful for family screening. ACE, angiotensin-converting enzyme; ARB, angiotensin receptor blocker.