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HelpTest Code PEWE Porphyrins Evaluation, Washed Erythrocytes
Reporting Name
Porphyrin Evaluation, RBCUseful For
Preferred test for analysis of erythrocyte porphyrins
Establishing a biochemical diagnosis of erythropoietic protoporphyria, and X-linked dominant protoporphyria
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| PPFWE | Protoporphyrins, Fractionation, RBC | Yes | No |
Testing Algorithm
This test is recommended for screening patients for possible erythropoietic protoporphyria and X-linked dominant protoporphyria. In addition, it can be used for evaluation of iron-deficiency anemia and chronic lead intoxication. Testing begins with total erythrocyte porphyrins. If the result is below 80 mcg/dL, it is normal, and testing is complete.
If the total erythrocyte porphyrin value is 80 mcg/dL or above, the protoporphyrin fractionation assay will automatically be performed at an additional charge. The fractionation test results include noncomplexed (free) protoporphyrin and zinc-complexed protoporphyrin.
The following algorithms are available:
Method Name
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Washed RBCOrdering Guidance
This is the preferred test for assessment for protoporphyria. The preferred test for assessing lead toxicity in children is blood lead. For more information see PBDV / Lead, Venous, with Demographics, Blood or PBDC / Lead, Capillary, with Demographics, Blood. The preferred screening test for suspicion of a hepatic porphyria is urine porphyrins. For more information see PQNRU / Porphyrins, Quantitative, Random, Urine.
Necessary Information
1. Volume of packed cells and total volume of specimen (red cells + saline) are required and must be sent with specimen.
2. Include a list of medications the patient is currently taking.
Specimen Required
All porphyrin tests on erythrocytes can be performed on 1 draw tube.
Patient Preparation: Patient must not consume any alcohol for 24 hours before specimen collection.
Collection Container/Tube:
Preferred: Green top (sodium heparin)
Acceptable: Dark blue top (metal free heparin), green top (lithium heparin), or lavender top (EDTA)
Submission Container/Tube: Plastic vial
Specimen Volume: Entire washed erythrocyte suspension
Collection Instructions: Collect and process whole blood specimen as follows:
1. Transfer entire specimen to a 12-mL graduated centrifuge tube.
2. Centrifuge specimen at 4° C for 10 minutes at 2000 rpm.
3. Record volume of packed cells and the total volume of the specimen.
4. Discard supernatant plasma.
5. Wash packed erythrocytes 2 times by resuspension of at least an equal amount of cold 0.9% saline, mix, and centrifuge for 5 minutes at 2000 rpm, discarding supernatant after each washing.
6. Resuspend packed cells to the original total volume with 0.9% saline. Invert specimen gently to mix.
7. Transfer to a plastic tube and freeze.
Specimen Minimum Volume
1 mL of washed and resuspended erythrocytes
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Washed RBC | Frozen (preferred) | 14 days | |
| Refrigerated | 14 days |
Reject Due To
| Cell suspension not available | Reject |
Special Instructions
Reference Values
PORPHYRINS, TOTAL, RBC
<80 mcg/dL
Day(s) Performed
Monday through Friday
CPT Code Information
84311-Spectrophotometry, analyte not elsewhere specified
82542-Chromatography (if appropriate)
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| PEWE | Porphyrin Evaluation, RBC | 2814-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 31942 | Total Porphyrins, RBC | 2814-2 |
| 31943 | Interpretation | 59462-2 |
| BG569 | Total cell suspension | 94496-7 |
| BG570 | Packed cell volume | 94497-5 |
Clinical Information
The porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Depending on the specific enzyme involved, various porphyrins and their precursors accumulate in different specimen types. The patterns of porphyrin accumulation in erythrocytes and plasma and excretion of the heme precursors in urine and feces allow for the detection and differentiation of the porphyrias.
Testing erythrocyte porphyrin level is most informative for patients with a clinical suspicion of erythropoietic protoporphyria (EPP) or X-linked dominant protoporphyria (XLDPP). Clinical presentation of EPP and XLDPP is identical with onset of symptoms typically occurring in childhood. Cutaneous photosensitivity in sun-exposed areas of the skin generally worsens in the spring and summer months. Common symptoms may include itching, edema, erythema, stinging or burning sensations, and occasionally scarring of the skin in sun-exposed areas. Although genetic in nature, environmental factors exacerbate symptoms, significantly impacting the severity and course of disease.
Erythropoietic protoporphyria is caused by decreased ferrochelatase activity resulting in significantly increased free protoporphyrin levels in erythrocytes, plasma, and feces.
X-linked dominant protoporphyria is caused by gain-of-function variants in the C-terminal end of ALAS2 gene and results in elevated erythrocyte levels of free and zinc-complexed protoporphyrin, and total protoporphyrin levels in plasma and feces.
Protoporphyrin fraction is the main component of erythrocyte porphyrins. When total erythrocyte porphyrins are elevated, fractionation and quantitation of zinc-complexed and free protoporphyrin are necessary to differentiate the inherited porphyrias from other causes of elevated porphyrin levels. Other possible causes of elevated erythrocyte zinc-complexed protoporphyrin may include:
-Iron-deficiency anemia, the most common cause
-Chronic intoxication by heavy metals (primarily lead) or various organic chemicals
-Congenital erythropoietic porphyria, a rare autosomal recessive porphyria caused by deficient uroporphyrinogen III synthase
-Hepatoerythropoietic porphyria, a rare autosomal recessive porphyria caused by deficient uroporphyrinogen decarboxylase
Typically, the workup of patients with a suspected porphyria is most effective when following a stepwise approach. See Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm or call 800-533-1710 to discuss testing strategies.
There are 2 test options:
-PEE / Porphyrins Evaluation, Whole Blood
-PEWE / Porphyrins Evaluation, Washed Erythrocytes.
The whole blood option is easiest for clients but requires that the specimen arrive at Mayo Clinic Laboratories within 7 days of collection. When this cannot be ensured, washed frozen erythrocytes, which are stable for 14 days, should be submitted.
Interpretation
Abnormal results are reported with a detailed interpretation which may include an overview of the results and their significance, a correlation to available clinical information provided with the specimen, differential diagnosis, and recommendations for additional testing when indicated and available.
Cautions
Alcohol suppresses enzyme activity potentially leading to false-positive results if it is ingested within 24 hours of specimen collection.
Method Description
This evaluation is performed as a 2-step analysis. First, the total red blood cells (RBC) porphyrin concentration is determined by extracting the porphyrins from washed, resuspended RBCs using a mixture of ethyl acetate and acetic acid. The porphyrins are then back extracted into dilute hydrochloric acid. Total porphyrins are quantified using this extract via spectrofluorometry.(Piomelli S. Free erythrocyte porphyrins in the detection of undue absorption of Pb and Fe deficiency. Clin Chem. 1977;23:264-269; Gou EE, Balwani M, Bissell DM, et al. Pitfalls in erythrocyte protoporphyrin measurement for diagnosis and monitoring of protoporphyrias. Clin Chem. 2015;61[12]:1453-1456. doi:10.1373/clinchem.2015.245456)
If the total porphyrin concentration is elevated, the RBCs are re-extracted to separate and quantify the zinc-complexed and noncomplexed (free) protoporphyrin via high-performance liquid chromatography.(Smith RM, Doran D, Mazur M, Bush B. High-performance liquid chromatographic determination of protoporphyrin and zinc protoporphyrin in blood. J Chromatogr. 1980 Mar;181[3-4]:319-327; Gou EE, Balwani M, Bissell DM, et al. Pitfalls in erythrocyte protoporphyrin measurement for diagnosis and monitoring of protoporphyrias. Clin Chem. 2015;61[12]:1453-1456. doi:10.1373/clinchem.2015.245456)