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HelpTest Code UPGDW Uroporphyrinogen Decarboxylase (UPG D), Washed Erythrocytes
Reporting Name
UPG Decarboxylase, RBCUseful For
Diagnosis of porphyria cutanea tarda type II and hepatoerythropoietic porphyria
Testing Algorithm
The following algorithms are available in Special Instructions:
-Porphyria (Acute) Testing Algorithm
-Porphyria (Cutaneous) Testing Algorithm
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
Washed RBCAdvisory Information
This test should only be ordered when the specimen will be received at Mayo Clinic Laboratories within 24 hours of collection. The preferred test for analysis of UPGD enzyme is UPGD / Uroporphyrinogen Decarboxylase (UPG D), Whole Blood.
Porphyria cutanea tarda (PCT) type I, the most common form of PCT, exhibits normal RBC enzyme activity. The preferred test for diagnosis is PQNU / Porphyrins, Quantitative, 24 Hour, Urine or PQNRU / Porphyrins, Quantitative, Random, Urine.
Specimen Required
All porphyrin tests on erythrocytes can be performed on 1 draw tube.
Patient Preparation: Patient should abstain from alcohol for 24 hours. Abstinence from alcohol is essential for at least 24 hours as alcohol suppresses enzyme activity for 24 hours after ingestion.
Collection Container/Tube:
Preferred: Green top (heparin)
Acceptable: Lavender top (EDTA)
Submission Container/Tube: Plastic vial
Specimen Volume: Washed erythrocyte suspension
Collection Instructions: Collect and process whole blood specimen as follows:
1. Immediately place specimen on wet ice.
2. Transfer entire specimen to a 12-mL graduated centrifuge tube.
3. Centrifuge specimen for 10 minutes at 2,000 rpm.
4. Record volume of packed cells and the total volume of the specimen.
5. Discard supernatant plasma.
6. Wash erythrocytes 2 times by resuspension with 5 mL of cold 0.9% saline, discarding supernatant after each washing.
7. Resuspend packed cells to the original total volume with 0.9% saline. Invert specimen gently to mix.
Specimen Minimum Volume
1 mL of washed and resuspended erythrocytes
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Washed RBC | Frozen | 24 hours |
Special Instructions
Reference Values
>1.0 Relative Units (normal)
0.80-0.99 Relative Units (indeterminate)
<0.80 Relative Units (porphyria cutanea tarda or hepatoerythropoietic porphyria)
Day(s) and Time(s) Performed
Tuesday; 8 a.m.
CPT Code Information
82657
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| UPGDW | UPG Decarboxylase, RBC | 49596-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 31892 | UPG Decarboxylase, RBC | 49596-0 |
Clinical Information
The porphyrias are a group of inherited disorders resulting from enzyme defects in the heme biosynthetic pathway. Porphyria cutanea tarda (PCT) is the most common porphyria resulting from a partial deficiency of hepatocyte and/or erythrocyte uroporphyrinogen decarboxylase (UROD). PCT is classified into 3 subtypes. The most frequently encountered is type I, a sporadic or acquired form, typically associated with concomitant disease or other precipitating factors. Patients exhibit normal UROD activity in erythrocytes but decreased hepatic activity. This differs from type II PCT in which patients exhibit approximately 50% activity in both erythrocytes and hepatocytes. Type II accounts for about 20% of cases and is inherited in an autosomal dominant manner with low penetrance. Type III is a rare familial form seen in less than 5% of PCT cases. As in type I, patients with type III PCT have normal UROD activity in erythrocytes with decreased hepatic activity. Type III cases are distinguished from type I by the history of other affected family members.
Hepatoerythropoietic porphyria (HEP) is a rare autosomal recessive form of porphyria that typically presents in early childhood. Patients have a severe deficiency of UROD, with activity levels 10% of normal in both hepatocytes and erythrocytes.
All forms of PCT and HEP result in accumulation of uroporphyrin and intermediary carboxyl porphyrins in skin, subcutaneous tissues, and the liver. The most prominent clinical characteristics are cutaneous photosensitivity and scarring on sun-exposed surfaces. Patients experience chronic blistering lesions resulting from mild trauma to sun-exposed areas. These fluid-filled vesicles rupture easily, become crusted, and heal slowly. Secondary infections can cause areas of hypo- or hyperpigmentation or sclerodermatous changes and may result in the development of alopecia at sites of repeated skin damage. Liver disease is common in patients with PCT as evidenced by abnormal liver function tests and with 30% to 40% of patients developing cirrhosis. In addition, there is an increased risk of hepatocellular carcinoma.
The workup of patients with a suspected porphyria is most effective when following a stepwise approach. See Porphyria (Cutaneous) Testing Algorithm in Special Instructions or call 800-533-1710 to discuss testing strategies.
Analytic Time
3 days (Not reported on Saturday or Sunday)Reject Due To
|
Hemolysis |
NA |
|
Lipemia |
NA |
|
Icterus |
NA |
|
Other |
NA |
NY State Approved
YesMethod Name
High-Performance Liquid Chromatography (HPLC)/Incubation of Lysed Erythrocytes
Forms
1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:
-Informed Consent for Genetic Testing (T576)
-Informed Consent for Genetic Testing-Spanish (T826)
2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.