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Porphyria Educational Services

Vol. 1 No. 46 ~ November 7, 1999
FOCUS:     Disorders Of Porphyrin Metabolism

Sometimes trying to understand porphyria is like reaching to
the heavens and grasping a star, or at best a close circling satallite.  For
many it is almost impossible to understand the complex terminology used.

So,  just how are the disorders of porphyrin metabolism diagnosed?

Each type of porphyria is defined by specific symptoms and diagnostic signs or
"markers," although these overlap considerably in some types.

If a disorder of porphyrin metabolism is suspected on the basis of
symptoms, diagnostic tests are usually ordered of urine and stool and
sometimes also of blood and plasma to look for characteristic abnormalities
of enzyme(s), porphyrin(s) and/or porphyrin "precursors".

These precursors are substances which are  called ALA
and PBG, and which are measured to check the activity of the first two
enzymes in the heme pathway.

If acute porphyria is suspected, this testing must be done
when  the patient's symptoms are worse than usual. Chemically-acquired
porphyrinopathies are more variable and often mimic one or more elements of
the different inherited types, but they can be tested and treated in the same way.

Since ALA and PBG are always elevated in urine during acute
attacks, these porphyrin precursors are sometimes used alone for screening
potential cases.

They may normal, however, in latent cases as well as those
in remission, in between attacks, and/or those with more chronic symptoms.
They also cannot distinguish between different types of porphyrinopathy.

To be definitively diagnosed, an active case of inherited porphyria or
acquired porphyrinopathy should show evidence of all the following:

1. Abnormal enzyme activity in one or more of the eight
porphyrin enzymes. Even if the patient has never had symptoms, [meaning that
they have remained latent] this alone is enough to diagnosis a latent case of porphyria.

2. Abnormal levels of porphyrins and/or porphyrin precursors
in the urine, stool, blood and/or plasma (although they may be so only
during acute attacks).

3. Acute and/or chronic symptoms typical of porphyrinopathies that are
not explainable by other diseases or other forms of chemical injury.