Complement 3 (C3) Test

Your doctor may order a C3 test if you show symptoms associated with the connective tissue, kidney or joint like:

• Glomerulonephritis (inflammation of the kidney due to an immune reaction) 
• Vasculitis (inflammation of blood vessels) 

If you suffer from repeated infections, your doctor may suspect an immunodeficiency disorder, especially lupus and order the C3 test.

Some symptoms of lupus include:

• Ulcers in the mouth and nose
• Hair loss
• Swelling around the eyes and in the feet and hands
• Joint pain
• Fatigue
• Butterfly-shaped rash on the cheeks
• Chest pain on taking deep breaths

A C3 test is also done to monitor disease progression and the progress of treatment of autoimmune disorders.

You do not need any special preparation for this test. Please inform your doctor if you are taking any medications including non-prescription drugs, vitamins and herbal supplements.

Since high levels of lipids and haemoglobin in the sample can affect the results of this test, inform your doctor if you have any known health conditions before sample collection.

A simple protocol is followed for sample collection. A sterile needle is used to draw a small amount of blood from a vein in the arm. You may feel slight pain as the needle goes into the arm. However, it will fade away quickly. The laboratory technician will deposit the sample in a special container, label it and send it to the lab for testing. 

Some people notice slight bruising at the site of needle insertion after the test - it’ll subside on its own. If the bruise does not disappear, please inform your doctor.

Normal results:

Normal values of C3 in the blood range between 0.68 and 1.80 g/L (grams per litre). These values mean that your symptoms are not due to changes in C3 levels. 

It is important to note that this normal range may vary from one laboratory to the other. The values obtained in the test also depend on the gender, age and medical history of the person. 

Abnormal results:

If the values obtained from the test are outside the normal range, it may be due to an underlying condition. There are two possible scenarios - the value can either be lower or higher than normal. Both high and low values are known to be associated with certain disorders.

Levels of C3 protein tend to be low in case of:

• Active lupus
• Inherited C3 deficiency (runs in the family) 
• Acquired C3 deficiency (occurs due to infections)
• Alcoholic liver disease, a less common cause
• Recurrent bacterial infections
• Certain types of kidney disorders

Higher than normal levels of C3 protein may occur after an infection or an injury.

Your doctor may prescribe an appropriate treatment to bring C3 levels back to normal. Repeat tests may be ordered after a while depending on the results.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.