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C4 level How the Test is Performed:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet 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 .
The sample is then sent to the laboratory where the quantity of C4 is measured.
How to Prepare:
There are no special preparations.
How it Feels:
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 .
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.
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Why this Test is Performed:
Complement activity ( CH50 , CH100 , terminal complement component, or individual complement proteins ) is measured to determine if complement is involved in the development of a number of diseases. Complement activity is also measured to monitor severity of a disease or determine efficiency of treatment. For example, patients with active lupus erythematosus may have depressed levels of C3 and C4, and these component levels may be followed as a rough index of disease activity.
Normal Values:
- males: 12 to 72 mg/dl (120 to 720 mg/L)
- females: 13 to 75 mg/dl (130 to 750 mg/L)
Note: mg/dl = milligrams per deciliter
Abnormal Results:
Increased complement activity may be seen in: Decreased complement activity may be seen in:
Cost:
The costs are:
$66 for a CH50 test
$47 for a CH100 test
$37 for a Complement 4 test
$86 for a serum complement test
Special Considerations:
Serum complement comprises a group of proteins that facilitate immunological and inflammatory responses. The so-called complement cascade involves a series of enzymatic reactions that take place in the blood. There are 9 major components labeled C1 through C9. The cascade can be initiated by various means, especially antigen-antibody complexes. The end-product of the cascade is the so-called membrane attack unit (also called terminal complement component), which creates holes in the membranes of attacking microorganisms, thereby causing lysis and death of the cells. CH50 or CH100 are 50% or 100% of 'whole' complement activity. There are also a number of side products of the complement cascade that attract white blood cells and increase the efficiency to engulf bacteria by phagocytic white blood cells.
When many microorganisms are exposed to fresh serum, complement is activated by an "alternative pathway" that does not require the presence of specific antibodies to the microorganism. These organisms are able to bind C3 directly. Bound C3, or some modified form of C3, is able to associate with factor D, factor B, and properdin to form a stable unit capable of continuing the complement cascade.
Typically, other tests that are more specific for the suspected disease are performed first.
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