 The urine screening test has been known to fail in the initial stages of a severe, life-threatening attack of acute intermittent porphyria.Up to 90% of the genetic carriers of the more common, dominantly inherited acute hepatic porphyrias (acute intermittent porphyria, hereditary coproporphyria, variegate porphyria) have been noted in DNA tests to be latent for classic symptoms and may require DNA or enzyme testing.The exception to this may be latent post-puberty genetic carriers of hereditary coproporphyria.