Laboratory findings in acute intermittent porphyria

During an acute attack large amounts of ALA and PEG are excreted in the urine, together with a moderate increase in uroporphyrin. The presence of PEG can be easily demonstrated by the addition of Erhlich s aldehyde reagent, the red complex formed being insoluble in n-butanol (now used in preference to chloroform). The red colour which forms spontaneously in the urine of patients with acute intermittent porphyria during an attack is due to the formation of porphobilin and porphyrins from the spontaneous condensation of PEG. Faecal porphyrins are usually normal, or only very slightly elevated. 

The liver, but not erythropoietic tissue, contedns large amounts of PEG, and there is evidence of hepatocellular dysfunction in a proportion of patients abnormal bromsulphthalein retention due to defective conjugation and excretion is occasionally seen [94], but elevation of serum bilirubin and alkaline phosphatase arc more common. 

An acute attack may be accompanied by hyponatraemia, hypochloraemia and oliguria, and this is almost cert2iinly due to inappropriate antidiuretic hormone secretion [98, 99, 100, 101] which may also account for the hypomagnesaemia which has also been described [101, 102]. 

Increased levels of protein-bound iodine and thyroxine have been reported [103, 104], but their significance is not yet known. 

The interactions of organo-phosphorus compounds such as DFP and related substances vsdth esterases have been most fully worked out in relation to the cholinesterases, and it is clear that the early, acute phases of intoxication by these compounds are associated with a profound inhibition of cholinesteraise activity. Inhibition of these enzymes is thought to be the result of the phosphorylation of the enzyme protein by the toxic agent  

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