Porphyria laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
Porphyrin studies
Electrolyte and Biomarker Studies
Increased urinary porphobilinogen (PBG) is diagnostic. δ-aminolevulinate (ALA) is somewhat increased. ALA-D will only have an elevation of ALA. A negative test rules out porphyria. The results can be confirmed with a quantitative test for fecal and plasma porphyrins and a 24 hour urine sample. The type of acute porphyria is determined based on measurement of fecal and plasma porphyrins. Hereditary coproporphyria (HCP) and Variegate porphyria (VP) will have coproporphyrin III in feces. VP will also have protoporphyrin and plasma will have an emission peak at 624-26 nm on fluorescence spectroscopy.
Porphyria is diagnosed through spectroscopy and biochemical analysis of blood, urine, and stool.[1] In general, urine estimation of porphobilinogen (PBG) is the first step if acute porphyria is suspected. As a result of feedback, the decreased production of heme leads to increased production of precursors, PBG being one of the first substances in the porphyrin synthesis pathway.[2] In nearly all cases of acute porphyria syndromes, urinary PBG is markedly elevated except for the very rare ALA dehydratase deficiency or in patients with symptoms due to lead poisoning or hereditary tyrosinemia type I.
Repeat testing during an attack and subsequent attacks may be necessary in order to detect a porphyria, as levels may be normal or near-normal between attacks. The urine screening test has been known to fail in the initial stages of a severe life threatening attack of acute intermittent porphyria.
The bulk (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 postpuberty genetic carriers of hereditary coproporphyria.
As most porphyrias are rare conditions, general hospital labs typically do not have the expertise, technology or staff time to perform porphyria testing. In general, testing involves sending samples of blood, stool and urine to a reference laboratory.[1] All samples to detect porphyrins must be handled properly. Samples should be taken during an acute attack, otherwise a false negative result may occur. Samples must be protected from light and either refrigerated or preserved.[1]
Hyponatremia (thought to be caused by ADH) can be severe.
Additional tests
Further diagnostic tests of affected organs may be required, such as nerve conduction studies for neuropathy or an ultrasound of the liver. Basic biochemical tests may assist in identifying liver disease, hepatocellular carcinoma, and other organ problems.
References
- ↑ 1.0 1.1 1.2 Thadani H, Deacon A, Peters T. Diagnosis and management of porphyria. BMJ 2000;320:1647-51. Fulltext. PMID 10856069.
- ↑ Anderson KE, Bloomer JR, Bonkovsky HL, Kushner JP, Pierach CA, Pimstone NR, Desnick RJ. Recommendations for the diagnosis and treatment of the acute porphyrias. Ann Intern Med 2005;142:439-50. PMID 15767622.