Laboratory Studies
Demonstration of elevated porphyrins in plasma (particularly for congenital erythropoietic porphyria [CEP]), urine, and stool is very useful for diagnosis of the porphyrias. [8, 9]
Qualitative urine examination can identify urine porphyrins. However, normal urine contains porphyrins, making comparison with a control sample essential. In both the amyl alcohol and talc tests, the urine must be adjusted to a pH of 4 by mixing 3 mL of urine with 1 mL of 1 mol/L acetate buffer.
For the amyl alcohol test, 4 mL of amyl alcohol is added to the 4-mL buffered urine solution. After vigorous shaking or low-speed centrifuge, the mixture is examined under a Wood lamp. [32] A pink-to-red fluorescence in the upper organic layer indicates a positive result.
For the talc test, 100 mg of talc is added to 10 mL of the buffered urine solution and shaken vigorously. Low-speed centrifuge for about 10 minutes produces a talc pellet, which can be examined under a Wood lamp. A pink or red color indicates a positive result.
Protoporphyria can be diagnosed by identifying numerous fluorescent erythrocytes in blood examined microscopically with a 100-watt iodine-tungsten lamp.
Qualitative stool studies can help guide the diagnosis. Mix 1-2 g of stool in 2 mL of an amyl alcohol, glacial acetic acid, and ether mixture. Red fluorescence under a Wood lamp indicates that porphyrins are present.
Stool porphyrin levels that are combined with other laboratory values and clinic correlation help guide the diagnosis. However, levels of porphyrins widely vary, and, in most cases, exact values for each disorder have not been established.
Table 3. Quantitative Fecal Porphyrins by Type of Porphyria (Open Table in a new window)
Porphyrin Type |
CEP |
PCT |
HCP |
VP |
EPP |
Uroporphyrin |
Significantly increased |
Increased |
Within reference range |
Within reference range |
Within reference range |
Coproporphyrin |
Significantly increased |
Increased |
Significantly increased |
Increased |
Within reference range |
Protoporphyrin |
Within reference range |
Within reference range |
Increased |
Significantly increased |
Significantly increased |
Quantitative urine porphyrin levels can be useful, but prior qualitative urine testing is desirable. Although hereditary coproporphyria (HCP) and variegate porphyria (VP) have identical urine porphyrin profiles, stool porphyrin testing can differentiate them. CEP and porphyria cutanea tarda (PCT) also have identical porphyrin patterns; however, erythrocyte examination results are positive only for CEP.
Table 4. Quantitative Urine Porphyrins (Open Table in a new window)
Porphyrin type |
CEP and PCT |
HCP and VP |
5-Aminolevulinate |
Within reference range |
Significantly increased |
PBG |
Within reference range |
Significantly increased |
Uroporphyrin |
Significantly increased |
Increased |
Coproporphyrin |
Increased |
Significantly increased |
Iron overload is almost always present in PCT and is reflected by abnormally high serum iron levels, low total iron-binding capacity, and high serum ferritin levels. Hemolytic anemia with polychromasia, poikilocytosis, anisocytosis, and basophilic stippling is observed in CEP. Thrombocytopenia and leukopenia are observed if hypersplenism develops in CEP.
Functional enzyme assays are not widely available and, therefore, are not commonly used in cutaneous porphyria diagnosis. ALAD and AIP assays are useful, and, at specialized centers, assays for other cutaneous porphyria types (eg, coproporphyrinogen oxidase) may be available. Although these other enzyme assays may be available, differential tissue expression of the enzymes makes these assays less useful in some individuals and they are not reliable for diagnostic purposes.
Many genetic defects responsible for porphyria have been identified. However, in general, a large number of defects account for each porphyria type, limiting the practical use of these tests. For example 121 mutations in the PPOX gene result in VP. In the future, advances in microarray technology may make routine DNA testing for multiple mutations possible. Currently, genetic testing is useful in 2 situations, as follows:
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If a genetic defect is known to be present in an individual, family members can be tested for the defect.
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Certain ethnic groups have a high incidence of a particular mutation (founder effect). For example, many South African families demonstrate a specific mutation for VP, and in the Swiss most VP patients show a single PPOX gene mutation. [33] Similarly, a limited number of mutations account for CEP in the United Kingdom. [34]
Imaging Studies
In CEP, single-photon emission computed tomography (SPECT) scanning may identify perfusion defects of the brain that were missed by magnetic resonance imaging (MRI). [35]
Procedures
Skin biopsy is not routinely indicated for the diagnosis of cutaneous porphyria and may lead to further scarring and poor healing.
Histologic Findings
Porphyria cutanea tarda
Skin lesions examined under light microscopy reveal subepidermal bullae with dermal papillae at the bases, elastosis and periodic acid-Schiff (PAS)-positive vessels in the dermis, and acid mucopolysaccharides at the dermal-epidermal junction. Immunofluorescence reveals accumulation of immunoglobulin G (IgG) and immunoglobulin M (IgM) and complement around dermal vessels and at the dermal-epidermal junction. [36]
Liver tissue reveals siderosis, fatty changes, necrosis, chronic inflammatory changes, and granuloma formation. Red autofluorescence and needlelike inclusion bodies are also observed. Cirrhosis and neoplastic changes are not uncommon.
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The heme production pathway. Heme production begins in the mitochondria, proceeds into the cytoplasm, and is then resumed in the mitochondria for the final steps. This figure outlines the enzymes and intermediates involved in the porphyrias. Enzymes names are presented in the boxes. Names of the intermediates are outside the boxes, between arrows. Multiple arrows leading to a box demonstrate that multiple intermediates are required as substrates for the enzyme to produce one product.
Tables
Type of Porphyria |
Age of Onset |
Incidence per 100,000 Population |
Male-to-Female Ratio |
CEP |
Infancy to early childhood; rare in adults |
300 cases total |
1:1 |
PCT |
Type I: Adulthood Type II (heterozygous mutations): Adulthood Type III (homozygous mutations): Childhood |
United States: 4 United Kingdom: 0.05 |
1:1 |
HCP |
Predominantly adulthood Youngest report was child aged 4 y |
Japan: 1.5 Czech: 1.5 Israel: 0.7 Denmark: 0.05 |
1:20 1:4 2:1 1:1 |
VP |
Heterozygous mutation: After puberty Homozygous mutation: Childhood (rare) |
South Africa: 34 |
1:1 |
EPP |
Infancy to childhood |
0.02 |
1:1 |
Porphyria |
Deficient Enzyme |
Location |
Inheritance |
Chromosome Band |
CEP |
Uroporphyrinogen III synthase |
Cytosol |
Autosomal recessive (AR) |
10q25.3-26.3 |
PCT |
Uroporphyrinogen decarboxylase |
Cytosol |
Autosomal dominant (AD) |
1p34 |
HEP |
Uroporphyrinogen decarboxylase |
Cytosol |
AR |
1p34 |
HCP |
Coproporphyrinogen oxidase |
Mitochondrial |
AD |
3q12 |
VP |
Protoporphyrinogen oxidase |
Mitochondrial |
AD |
1q22-23 |
EPP |
Ferrochelatase |
Mitochondrial |
AD, AR |
18q22 |
Porphyrin Type |
CEP |
PCT |
HCP |
VP |
EPP |
Uroporphyrin |
Significantly increased |
Increased |
Within reference range |
Within reference range |
Within reference range |
Coproporphyrin |
Significantly increased |
Increased |
Significantly increased |
Increased |
Within reference range |
Protoporphyrin |
Within reference range |
Within reference range |
Increased |
Significantly increased |
Significantly increased |
Porphyrin type |
CEP and PCT |
HCP and VP |
5-Aminolevulinate |
Within reference range |
Significantly increased |
PBG |
Within reference range |
Significantly increased |
Uroporphyrin |
Significantly increased |
Increased |
Coproporphyrin |
Increased |
Significantly increased |
