All porphyria diagnoses are confirmed by biochemical testing. “Clinical diagnoses” without positive biochemical results are not considered diagnostic of porphyria.
Screening tests (i.e. first line testing) is not the same for all porphyrias. Testing must be tailored to the presenting symptoms and the type of porphyria suspected.
Table 1. Symptom-Based First-line Testing
|Acute attacks of severe abdominal pain, nausea, vomiting, rapid heartbeat and other symptoms.||
Spot urine porphobilinogen (PBG) and total porphyrins
*Obtain sample when symptoms are present, if possible
Note- urine PBG is generally not included in urine total porphyrin tests
|Blistering skin photosensitivity (with or without acute attack symptoms)||Plasma total porphyrins and urine total porphyrins|
|Non-blistering photosensitivity||Erythrocyte protoporphyrin and plasma total porphyrins|
An AHP should be suspected if a patient presents with neurovisceral signs and symptoms and an initial evaluation excludes more common causes. With the very rare exception of ADP porphyria, PBG is expected to be substantially increased in all patients during acute attacks but not in other medical conditions. Because concentrations of PBG in the urine depend in part upon how dilute the urine is, they are best expressed normalized to urinary creatinine concentrations [mg PBG/ g creat or mmol PBG/mol creatinine]. This test is both sensitive and specific. An exception is ADP, in which ALA and porphyrins, but not PBG, are elevated.
Measurement of urine PBG should be combined with total urine porphyrins for first line testing. This is recommended even though porphyrin elevation is nonspecific, because porphyrins may remain increased longer than PBG in AHPs (especially in HCP and VP). Urgent first line measurement of ALA is not essential, because ALA elevation from ADP or any other cause is always accompanied by increased porphyrins.
Normal urine PBG and total porphyrins essentially rules out an AHP as the cause of concurrent symptoms. However, slight elevations of PBG and porphyrins may not support a diagnosis of AHP, especially with more sensitive methods that result in a narrow reference range.
When marked elevation in PBG establishes a diagnosis of AHP, more extensive second line biochemical and/or genetic testing should be done to differentiate these conditions.
Elevation in urine porphyrins without elevation in PBG also requires further evaluation by second line testing, to include urine ALA and plasma and fecal porphyrins, which if normal will exclude ADP, HCP and VP.
Elevation of urine coproporphyrin only is not diagnostic, because it occurs in a number of other medical conditions, notably in heavy users of alcohol and/or liver disease. Elevation of ALA and coproporphyrin (with normal PBG) is typical of lead poisoning, which should be confirmed with a blood test for heavy metals (lead, mercury, arsenic).
Table 2. Second-line Biochemical Testing for AHPs: Laboratory Findings to Differentiate the four Acute Porphyrias
|Acute Porphyria||HMBS activity in RBCs||Urine PBG||Urine ALA||Urine porphyrins||Fecal porphyrins||Plasma porphyrins|
|AIP||Decreased in ~90% of cases||Variably elevated||Variably elevated||Increased; mostly uroporphyrin and coproporphyrin||Normal or slightly increased||Normal or slightly increased|
|HCP||normal||""||""||""||Markedly increased; mostly coproporphyrin III||Normal or slightly increased|
|VP||normal||""||""||""||Markedly increased; mostly coproporphyrin III and protoporphyrin||Markedly increased; Elevated, with fluorescence peak at ~626nm|
|ADP||normal||normal||""||Increased; mostly coproporphyrin III||Normal or slightly increased||Normal or slightly increased|
Labs that can be used for second-line testing include: UTMB, ARUP, Mayo, Quest, and LabCorp
Total plasma or urine porphyrins are measured when porphyrias are considered as a possible cause of blistering skin photosensitivity. Normal results effectively exclude these cutaneous porphyrias. Further second line testing is needed if porphyrins are increased, because this finding is not specific, and porphyrinuria (especially coproporphyrinuria) is common in other diseases. If second line testing is negative, then porphyria is not present.
Porphobilinogen (PBG) is normal and aminolevulinic acid (ALA) may be slightly elevated.
The porphyrin profile in plasma and urine is similar to what is seen in PCT. The diagnosis is confirmed by checking UROD activity level in red blood cells and by genetic testing.
Table 3. Laboratory Findings to Differentiate Blistering Cutaneous Porphyrias
|Porphyria||Urine porphyrins||Erythrocyte porphyrins||Plasma||Fecal porphyrins|
|PCT||Elevated; mostly uro- and heptacarboxyl porphyrin||Normal or slightly elevated||Elevated, with fluorescence emission peak 615-620nm||Normal or modest elevation with complex pattern including increased isocoproporphyrin|
|HEP||""||Elevated, mostly zinc protoporphyrin||""||Elevated with complex pattern including increased isocoproporphyrin|
|CEP||Increased; mostly uroporphyrin I and coproporphyrin I||Elevated, mostly uroporphyrin I and coproporphyrin I, or zinc proto porphyrin in milder cases||""||Elevated, mostly coproporphyrin I|
|VP*||Variable increases in ALA, PBG and porphyrins (usually mostly uroporphyrin and coproporphyrin||Normal or slightly elevated||Elevated, with fluorescence peak at ~626nm||Elevated, mostly coproporphyrin III and protoporphyrin|
|HCP*||""||""||Elevated, with fluorescence peak at 615-620 nm||Elevated, mostly coproporphyrin III|
*Elevation in plasma porphyrins with or without blistering skin lesions are common in VP, but uncommon in HCP in the absence of skin lesions.
Urine ALA, PBG and porphyrins are normal in these conditions. It is essential to measure erythrocyte total protoporphyrin to screen for EPP and XLP. Plasma porphyrins are also increased in most cases. Some major laboratories do not offer the proper testing for EPP and XLP. At present, only the UTMB Porphyria Lab and Mayo Medical Laboratories are recommended.
Table 4. Laboratory Findings in the Non-Blistering Cutaneous Porphyrias
|Porphyria||Urine porphyrins||Erythrocyte total protoporphyrin||Plasma porphyrins||Fecal porphyrins|
|EPP||Normal||Substantial elevation, >85% metal-free protoporphyrin||Usually elevated, with fluorescence peak at ~634 nm, but may be normal||Normal or modest elevation , mostly protoporphyrin|
|XLP||""||Substantial elevation, 50-85% metal-free protoporphyrin||""||""|
Confirmation of the diagnosis by genetic testing is recommended for all porphyrias. Importantly, knowing the familial mutation(s) enables screening of family members who may be at risk for developing symptoms or may pass a pathogenic mutation to the next generation. If the type of porphyria has been proven biochemically, it is usually necessary to examine only one gene to identify the responsible mutation. Once the familial mutation is known, the testing of family members can be targeted to that mutation.
Table 5. Genes Responsible for the Porphyrias
|Porphyria||Affected Enzyme||Sequence in pathway||Gene Symbol|
|XLP||Delta-aminolevulinic acid synthase-2||1||ALAS2|
|ADP||Delta-aminolevulinic acid synthase||2||ALAD|
|AIP||Hydroxymethylbilane synthase (porphobilinogen deaminase)||3||HMBS|
|CEP*||Uroporphyrinogen III synthase||4||UROS|
|PCT & HEP||Uroporphyrinogen decarboxylase||5||UROD|
*Very rarely CEP is due to a mutation in the X-linked GATA1 gene.