Sorted By Test Name - Mayo Medical Laboratories

ALAD
88924
Erythrocytes
Clinical Information: Porphyrias are a group of inherited disorders resulting from an enzyme
deficiency in the heme biosynthetic pathway. Delta-aminolevulinic acid (ALA) dehydratase (ALAD)
catalyzes the second step in heme synthesis, the condensation reaction of 2 molecules of ALA into
porphobilinogen (PBG). ALAD deficiency porphyria (ADP) results from a deficiency of ALAD, which
causes ALA accumulation in the body with subsequent excretion of excessive amounts in the urine. PBG
excretion remains normal, which rules out other forms of acute porphyria. ADP is an acute hepatic
porphyria that produces neurologic symptoms similar to those seen in acute intermittent porphyria.
Symptoms include acute abdominal pain, peripheral neuropathy, nausea, vomiting, constipation, and
diarrhea. Respiratory impairment, seizures, and psychosis are all possible during an acute period. ADP is
extremely rare. Only 7 cases have been identified and confirmed since it was first described in 1979. ADP
is inherited in an autosomal recessive manner. For additional information on the recommended order of
testing, the following algorithms are available in Special Instructions: -Porphyria (Acute) Testing
Algorithm -Porphyria (Cutaneous) Testing Algorithm For additional information, see The Heme
Biosynthetic Pathway in Special Instructions.
Useful For: Confirmation of a diagnosis of aminolevulinic acid dehydratase deficiency porphyria
Interpretation: In patients with deficiency porphyria (ADP), erythrocyte delta-aminolevulinic acid
(ALA) dehydratase (ALAD) activity is typically reduced by 80%, or more, from normal levels. ALAD
activity can be inhibited in other situations including hereditary tyrosinemia type 1, heavy metal
intoxication, and exposure to styrene, trichloroethylene, and bromobenzene. These causes should be ruled
out when considering a diagnosis of ADP.
Reference Values:
> or =4.0 nmol/L/sec
3.5-3.9 nmol/L/sec (indeterminate)