Coproporphyrin levels

Alternative names
Uroporphyrin levels; Protoporphyrin levels; Porphyrins - total; Porphyrins - blood

Definition

This test measures total red blood cell porphyrins.

Porphyrins are pigments found in animals and plants. They are involved in the formation of many important substances in the body including hemoglobin, which carries oxygen in the blood.

Coproporphyrin, protoporphyrin, and uroporphyrin are three porphyrins related to red blood cells, which can normally be measured in small amount in the human blood stream. Protoporphyrin is normally found in highest quantity and thus this test is also known as the PROTO test. Additional tests are needed to know the levels of specific porphyrins.

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
The sample is then placed in ice and taken immediately to the laboratory.

How to prepare for the test
Fasting for 12 to 14 hours prior to this test is required. You may drink water right before the test.

If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed
This test is used to diagnose porphyrin disorders involving red blood cells. In combination with other tests, this test is useful for diagnosing disorders such as lead poisoning and some neurologic and skin disorders.

Normal Values
This test specifically measures total porphyrin levels, but reference values (i.e., range of values seen in a group of “healthy” people) for the individual components are also included:

• total porphyrin levels: 16 to 60 mcg/dl
  
• coproporphyrin levels: < 2 mcg/dl
  
• protoporphyrin levels: 16 to 60 mcg/dl
  
• uroporphyrin levels: < 2 mcg/dl

Note: mcg/dl = micrograms per deciliter
It is important to recognize that these reference ranges will vary between different laboratories depending upon the way the test is performed. Individual results must therefore be interpreted accordingly.

What abnormal results mean
Increased levels of coproporphyrins may indicate:

• congenital erythropoietic porphyria
  
• sideroblastic anemia

Increased protoporphyrin levels may indicate:

• infection
  
• thalassemia
  
• sideroblastic anemia
  
• lead poisoning
  
• iron deficiency anemia
  
• erythropoietic anemia
  
• increased erythropoiesis

Increased uroporphyrin levels may indicate:

• congenital erythropoietic porphyria
  
• erythropoietic protoporphyria

What the risks are
Risks associated with having blood drawn are slight:

• excessive bleeding
  
• fainting or feeling light-headed
  
• Hematoma (blood accumulating under the skin)
  
• infection (a slight risk any time the skin is broken)
  
• multiple punctures to locate veins

Special considerations
Failure to comply with dietary restrictions prior to the test may alter and invalidate test results.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

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