Complement 4 Test is a blood test that measures the activity of a specific protein in the body.
What is a Complement 4 Test?
A Complement 4 Test may be used to observe a patient with an autoimmune disorder. The test also provides important information about the efficiency of existing treatment for an autoimmune condition. C3 and C4 are the most commonly measured complement components. Complement activity fluctuates throughout the body. 
Why is Complement 4 Test suggested?
The doctor may order a Complement 4 test if the patient is experiencing symptoms that indicate an autoimmune disease, which is as follows:
- Extreme fatigue.
- Muscle pain.
- Joint pain.
- Sudden and unexpected weight loss.
- Muscle weakness.
- Muscle paralysis.
How is the Complement 4 Test performed?
Blood is drawn from a vein in the Complement 4 Test. Usually, a vein from the inside of the elbow or the back of the hand is preferred. 
What are the parameters measured in the Complement 4 Test?
The normal range in Complement 4 Test is 15 to 45 milligrams per deciliter (mg/dL) (0.15 to 0.45 g/L).. Increased complement activity might indicate Cancer and Ulcerative colitis.
Decreased complement activity might be seen in Bacterial infections, Cirrhosis, Glomerulonephritis, Hepatitis, Hereditary angioedema, Kidney transplant rejection, Lupus nephritis, Malnutrition, Systemic lupus erythematosus, Rare inherited complement deficiencies. 
Preparation before performing Complement 4 Test
There is no special preparation needed prior Complement 4 Test.
Post-care after Complement 4 Test
Complement 4 Test is a simple procedure. No special care is required post the sample for testing has been given. A bandage may be required as blood is drawn.
Sample types in Complement 4 Test
A blood sample is taken in the Complement 4 Test.
Side effects/risks of Complement 4 Test
There are no risks associated with having blood drawn in the Complement 4 Test. The patient might feel lightheaded in the worst case scenario.