Definition

The complement component 4 (C4) test examines the amount of complement C4 circulating in the bloodstream through a simple blood test. C4 is a protein component of the complement system. This system consists of approximately 60 proteins that are present in blood plasma or on the surface of some cells.

Proteins work in conjunction with the immune system to fight infections by eliminating disease-causing bacteria and viruses. They assist in eliminating dead cells and foreign substances from the body. Occasionally, individuals may inherit a lack of certain complement proteins. These individuals are susceptible to specific infections or autoimmune diseases.

Your doctor can diagnose and monitor the therapy for some disorders by monitoring complement C4 levels, particularly in relation to other components of the complement system. Systemic lupus erythematosus (lupus) and rheumatoid arthritis are autoimmune illnesses that frequently exhibit abnormal C4 levels.

The complement C4 test requires relatively little preparation and poses few dangers. The laboratory will analyze your blood sample. Following this, your physician will receive and analyze the results.

We also have an article on C3 Complement Test which you can read here: C3 Complement Test - Definition, Indication and Contraindication.

Indication

Complement activity may be measured to diagnose autoimmune disorders and to determine how severe a disease is. Complement tests can also provide doctors with valuable information about the effectiveness of current treatment for an autoimmune condition.

The complement C4 test is one of the most frequently used complement component tests. Your doctor may order a complement C4 test if you’re experiencing symptoms that indicate an autoimmune disease, such as:

• Lupus, a chronic disease affecting multiple parts of the body, including the joints, blood vessels, kidneys, and brain
• Rheumatoid arthritis, a condition that causes pain and swelling of the joints, mostly in the hands and feet

Doctors may also order this test if they have concerns about your kidney function or if you have signs of chronic hepatitis. It may also be used to help diagnose certain bacterial, viral, or fungal infections.

Contraindication

There are no individuals for whom it is advised against to check their serum C4 protein level; everyone is eligible to undergo blood tests for monitoring the levels of C4 proteins in their bodies.

Preparations Prior to Test

The test can be conducted at a hospital, clinic, or laboratory. There is no need to prepare for this test. Ensure that your healthcare provider is aware of all medications, vitamins, supplements or herbs you are currently taking. This encompasses over-the-counter medications and any illicit substances you may consume. 

No dietary or pharmaceutical restrictions are required for a C4 test. Consult your healthcare practitioner about the necessity of fasting or medication modifications if you are undergoing additional tests simultaneously.

Test Procedures

A healthcare professional will extract a blood sample from a vein, usually in your arm, using a tiny needle. Once the needle is placed, a little sample of blood will be drawn into a test tube. You may experience a slight stinging sensation when the needle is inserted or removed.

Normal and Abnormal Values

Normal readings can vary among various laboratories, thus it is crucial to discuss with your doctor about your results. Typically, the normal range of C4 measurement for men is 12 to 72 mg/dL of blood. For women, the typical range is 13 to 75 mg/dL of blood.

High values indicate results above the reference range, while low values indicate results below the reference range. Occasionally, elevated results on the lab report are denoted as "high" or "H". Low values can also be indicated as "low" or "L". Consult your doctor to know whether your test result is considered normal or abnormal.

Results and Suggestions (Follow-Up Tests)

Various factors can cause fluctuations in C4 protein levels, leading to either low or high levels. Complement levels typically increase significantly following an infection or injury. Elevated C4 levels could indicate the presence of malignancy, ulcerative colitis, or inflammation. It could suggest that the immune system is reacting to a recent infection. 

Decreased complement C4 levels may suggest:

• Bacterial infections
• Malnutrition
• Hepatitis or inflammation of the liver
• Cirrhosis, is liver disease that signifies severe liver impairment
• Glomerulonephritis, is a form of renal illness
• Lupus nephritis, is a kidney illness commonly associated with SLE
• SLE (Systemic Lupus Erythematosus), an autoimmune condition impacting the skin, joints, kidneys, and other organs
• Hereditary angioedema is an uncommon yet severe illness characterized by swelling in several body areas

Low levels of complement C4 have also been associated with many types of kidney disease and chronic hepatitis. It has also been identified in some childhood illnesses, such as:

• Henoch-Schonlein purpura, a kind of vasculitis
• Pediatric diabetes mellitus

Consult to The Right Doctor

Test results can differ based on factors such as age, gender, medical history, or other factors such as the utilized laboratory. Consult your doctor or internist to interpret the implications of your test results.

Want to know information about the results of laboratory examinations, radiology, and others? Check here, yes!