Complement assay; Complement proteins
Complement is a blood test that measures the activity of certain proteins in the liquid portion of your blood.
A complement system is a group of proteins that move freely through your bloodstream. The proteins work with your immune system. They also play a role in the development of inflammation.
There are nine major complement proteins. They are labeled C1 through C9.
How the Test is Performed
A blood sample is needed. This is most often taken through a vein. The procedure is called venipuncture.
How to Prepare for the Test
There is no special preparation.
How the Test will Feel
When the needle is inserted to draw blood, some people feel slight pain, while others feel only a prick or sting. Afterward, there may be some throbbing.
Why the Test is Performed
Total complement activity (CH50, CH100) looks at the overall activity of the complement system. In most cases, other tests that are more specific for the suspected disease are done first. C3 and C4 are the complement components measured most often.
A complement test may be used to monitor people with an autoimmune disorder. It is also used to see if treatment for their condition is working. For example, people with active lupus erythematosus may have lower-than-normal levels of the complement proteins C3 and C4.
Complement activity varies throughout the body. For example, in people with rheumatoid arthritis, complement activity in the blood may be normal or higher-than-normal, but much lower-than-normal in the joint fluid.
People with gram-negative septicemia and shock often have very low C3 and components of what’s known as the alternative pathway. C3 is often also low in fungal infections and some parasitic infections such as malaria.
Normal Results
- Total blood complement level: 41 to 90 hemolytic units
- C1 level: 16 to 33 mg/dL (160 to 330 mg/L)
- C3 levels: 88 to 252 mg/dL (0.88 to 2.52 g/L) in males; 88 to 206 mg/dL (0.88 to 2.06 g/L) in females
- C4 levels: 12 to 72 mg/dL (0.12 to 0.72 g/L) in males; 13 to 75 mg/dL (0.13 to 0.75 g/L) in females
Note: mg/dL = milligrams per deciliter; mg/L = milligrams per liter
Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Increased complement activity may be seen in:
- Cancer
- Certain infections
- Ulcerative colitis
Decreased complement activity may be seen in:
- Cirrhosis
- Glomerulonephritis
- Hereditary angioedema
- Hepatitis
- Kidney transplant rejection
- Lupus nephritis
- Malnutrition
- Systemic lupus erythematosus
Risks
Risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Considerations
The “complement cascade” is a series of reactions that take place in the blood. The cascade activates the complement proteins. The result is an attack unit that creates holes in the membrane of bacteria, killing them.
Complement component 3 (C3)
C3
Complement C3 is a blood test that measures the activity of a certain protein that is part of the complement system. A complement system is a group of proteins that move freely through your bloodstream. The proteins work with your immune system and play a role in the development of inflammation.
There are nine major complement proteins. They are labeled C1 through C9. This test measures C3.
How the Test is Performed
Blood is drawn from a vein. Most often, a vein from the inside of the elbow or the back of the hand is used. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to Prepare for the Test
There is no special preparation needed.
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
C3 and C4 are the most commonly measured complement components.
A complement test may be used to monitor people with an autoimmune disorder and to see if treatment for their condition is working. When the complement system is turned on during inflammation, levels of complement proteins may go down. For example, patients with active lupus erythematosus may have lower-than-normal levels of the complement proteins C3 and C4.
Complement activity varies throughout the body. For example, in people with rheumatoid arthritis, complement activity in the blood may be normal or higher-than-normal, but much lower-than-normal in the joint fluid.
The test may also be done for the following conditions:
- Fungal infections
- Gram negative septicemia
- Parasitic infections, such as malaria
- Paroxysmal nocturnal hemoglobinuria (PNH)
- Shock
Normal Results
The normal range is 75 to 135 milligrams per deciliter (mg/dL) or 0.07 to 0.14 grams per liter (g/L).
Note: Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Increased complement activity may be seen in:
- Cancer
- Ulcerative colitis
Decreased complement activity may be seen in:
- Bacterial infections (especially Neisseria)
- Cirrhosis
- Glomerulonephritis
- Hepatitis
- Hereditary angioedema
- Kidney transplant rejection
- Lupus nephritis
- Malnutrition
- Systemic lupus erythematosus
Risks
Risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Considerations
The “complement cascade” is a series of reactions that take place in the blood. The cascade activates the complement proteins. A result is an attack unit that creates holes in the membrane of bacteria, killing them. C3 attaches to and kills bacteria directly.
Complement component 4
C4
Complement component 4 is a blood test that measures the activity of a certain protein that is part of the complement system. A complement system is a group of proteins that move freely through your bloodstream. The proteins work with your immune system and play a role in the development of inflammation.
There are nine major complement proteins. They are labeled C1 through C9. This test measures C4.
How the Test is Performed
Blood is drawn from a vein. Most often a vein from the inside of the elbow or the back of the hand is used. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to Prepare for the Test
No special preparation is needed.
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
C3 and C4 are the most commonly measured complement components. When the complement system is turned on during inflammation, levels of complement proteins may go down. Complement activity may be measured to determine how severe a disease is or if treatment is working.
A complement test may be used to monitor people with an autoimmune disorder. For example, people with active lupus erythematosus may have lower-than-normal levels of the complement proteins C3 and C4.
Complement activity varies throughout the body. In people with rheumatoid arthritis, complement activity may be normal or higher-than-normal in the blood, but much lower-than-normal in the joint fluid.
Normal Results
Normal ranges are:
- Males: 12 to 72 mg/dL (0.12 to 0.72 g/L)
- Females: 13 to 75 mg/dL (0.13 to 0.75 g/L)
Note: mg/dL = milligrams per deciliter (100 milliliters)
Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Increased complement activity may be seen in:
- Cancer
- Ulcerative colitis
Decreased complement activity may be seen in:
- Bacterial infections (especially Neisseria)
- Cirrhosis
- Glomerulonephritis
- Hepatitis
- Hereditary angioedema
- Kidney transplant rejection
- Lupus nephritis
- Malnutrition
- Systemic lupus erythematosus
Risks
Risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Complement fixation test to C burnetii
The complement fixation test to Coxiella burnetii ( C burnetti ) is a blood test that checks for infection due to a bacterium called C burnetii, which causes Q fever.
How the Test is Performed
A blood sample is needed.
The sample is sent to a laboratory. There, a method called complement fixation is used to check if the body has produced substances called antibodies to a specific foreign substance ( antigen ), in this case, C burnetii . Antibodies defend the body against bacteria, viruses, and fungi. If the antibodies are present, they stick, or “fix” themselves, to the antigen. This is why the test is called “fixation.”
How to Prepare for the Test
No special preparation is necessary for this test.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or bruising. This soon goes away.
Why the Test is Performed
This test is done to detect Q fever.
Normal Results
The absence of antibodies to C burnetii is normal. It means you do not have Q fever now or in the past.
What Abnormal Results Mean
An abnormal result means you have a current infection with C burnetii , or that you have been exposed to the bacteria in the past. People with past exposure may have antibodies, even if they are not aware that they were exposed. Further testing may be needed to distinguish between current, previous, and chronic infection.
During the early stage of an illness, few antibodies may be detected. Antibody production increases during the course of an infection. For this reason, this test may be repeated several weeks after the first test.
Risks
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.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
