How is variegate porphyria distinguished from porphyria cutanea tarda?

Variegate porphyria (VP) may produce cutaneous lesions that are indistinguishable from those seen in PCT, but patients with VP have increased levels of protoporphyrins in their stool and only moderately increased urine porphyrins. Unlike PCT patients, VP patients often have acute attacks of porphyria (gastrointestinal pain and neurologic deficits) similar to those seen in patients with acute intermittent porphyria, and thus it is important to distinguish VP from PCT.