Part of
Infection & inflammation
Part of
Infection & inflammation
Blood biomarker
Part of
Infection & inflammation
Complement Component 3 (C3)
Complement Component 3 (C3)
Complement component 3 (C3) is a protein of the immune system, helping to fight infections.
Complement component 3 (C3) is a protein of the immune system, helping to fight infections.
Complement Component 3 (C3)
Normal range
Normal range
0.8-1.6 g/L
0.8-1.6 g/L
Normal range
0.8-1.6 g/L
0.8-1.6 g/L
Normal range
Complement Component 3 (C3)
Complement Component 3 (C3)
Complement component 3 (C3) is a protein of the immune system, helping to fight infections.
Complement Component 3 (C3)
Normal range
0.8-1.6 g/L
Normal range
0.8-1.6 g/L
0.8-1.6 g/L
Normal range
Complement Component 3 (C3)
Complement Component 3 (C3)
Complement component 3 (C3) is a protein of the immune system, helping to fight infections.
Complement Component 3 (C3)
Normal range
0.8-1.6 g/L
Normal range
0.8-1.6 g/L
0.8-1.6 g/L
Normal range
Complement Component 3 (C3)
Dr. Jack Devin
MBBS
Your Immune System's Versatile Defender
Your Immune System's Versatile Defender
Deep within your immune system lies a powerful and complex network of proteins known as the complement system. At the heart of this network is Complement C3, the most abundant and crucial of these proteins. Think of it as an immune system multi-tool: it can tag invading pathogens for destruction, recruit other immune cells to the site of an infection, and directly attack and eliminate harmful bacteria.
C3 circulates in your blood in an inactive state, waiting for a trigger. When the body detects a threat, C3 is activated in a rapid cascade. Measuring the level of C3 in your blood provides a vital snapshot of this system's activity, offering clues about hidden inflammation, infection, or an underlying autoimmune condition.
Deep within your immune system lies a powerful and complex network of proteins known as the complement system. At the heart of this network is Complement C3, the most abundant and crucial of these proteins. Think of it as an immune system multi-tool: it can tag invading pathogens for destruction, recruit other immune cells to the site of an infection, and directly attack and eliminate harmful bacteria.
C3 circulates in your blood in an inactive state, waiting for a trigger. When the body detects a threat, C3 is activated in a rapid cascade. Measuring the level of C3 in your blood provides a vital snapshot of this system's activity, offering clues about hidden inflammation, infection, or an underlying autoimmune condition.
High C3 Levels: When the Immune System is on High Alert
High C3 Levels: When the Immune System is on High Alert
High C3 Levels: When the Immune System is on High Alert
Learn how C3 levels rise during acute inflammation and infection as your body ramps up its defences.
Read more
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
Discover why low C3 can indicate that the immune system is being over-consumed in a battle against chronic infection or an autoimmune disease.
Read more
C3's Role Beyond Infection: Autoimmunity and Kidney Health
C3's Role Beyond Infection: Autoimmunity and Kidney Health
C3's Role Beyond Infection: Autoimmunity and Kidney Health
Understand how C3 is critically involved in conditions like lupus and certain types of kidney disease, where the complement system mistakenly attacks the body's own tissues.
Read more
Understanding Your Results
Understanding Your Results
Understanding Your Results
Learn how doctors interpret your C3 level, often alongside C4 and other tests, to diagnose and monitor immune system activity.
Read more
High C3 Levels: When the Immune System is on High Alert
Elevated levels of Complement C3 are most often a sign of acute inflammation. C3 is what's known as an 'acute-phase reactant', meaning its production by the liver is significantly increased in response to an immediate threat. This is a normal and healthy part of the body's defence mechanism.
A spike in C3 can be seen during various conditions, including:
Acute infections: Bacterial or viral infections drive the liver to boost C3 production for enhanced pathogen clearance.
Injury or trauma: Significant injury or surgery triggers systemic inflammation and elevated C3.
Chronic inflammatory states: Obesity, metabolic syndrome, or some cancers may also cause mildly elevated C3 as part of ongoing low‑grade inflammation.
In these situations, the high C3 level reflects an immune system that is actively and appropriately responding to a challenge. The levels will typically return to normal once the underlying condition is resolved.
High C3 Levels: When the Immune System is on High Alert
Elevated levels of Complement C3 are most often a sign of acute inflammation. C3 is what's known as an 'acute-phase reactant', meaning its production by the liver is significantly increased in response to an immediate threat. This is a normal and healthy part of the body's defence mechanism.
A spike in C3 can be seen during various conditions, including:
Acute infections: Bacterial or viral infections drive the liver to boost C3 production for enhanced pathogen clearance.
Injury or trauma: Significant injury or surgery triggers systemic inflammation and elevated C3.
Chronic inflammatory states: Obesity, metabolic syndrome, or some cancers may also cause mildly elevated C3 as part of ongoing low‑grade inflammation.
In these situations, the high C3 level reflects an immune system that is actively and appropriately responding to a challenge. The levels will typically return to normal once the underlying condition is resolved.
High C3 Levels: When the Immune System is on High Alert
Elevated levels of Complement C3 are most often a sign of acute inflammation. C3 is what's known as an 'acute-phase reactant', meaning its production by the liver is significantly increased in response to an immediate threat. This is a normal and healthy part of the body's defence mechanism.
A spike in C3 can be seen during various conditions, including:
Acute infections: Bacterial or viral infections drive the liver to boost C3 production for enhanced pathogen clearance.
Injury or trauma: Significant injury or surgery triggers systemic inflammation and elevated C3.
Chronic inflammatory states: Obesity, metabolic syndrome, or some cancers may also cause mildly elevated C3 as part of ongoing low‑grade inflammation.
In these situations, the high C3 level reflects an immune system that is actively and appropriately responding to a challenge. The levels will typically return to normal once the underlying condition is resolved.
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
While high levels indicate production, low levels of C3 (hypocomplementaemia) often suggest that the complement system is being used up faster than it can be replaced. This 'consumption' is a key indicator that the immune system is engaged in a prolonged battle.
The most common causes of low C3 are autoimmune diseases. In conditions like Systemic Lupus Erythematosus (SLE), the complement system is mistakenly activated and directed against the body's own cells and tissues, leading to a continuous drain on C3 levels. A low C3 in someone with lupus can signal a disease flare-up, particularly involving the kidneys.
Other causes of low C3 include:
Chronic Infections: Persistent infections can lead to ongoing complement consumption.
Genetic Deficiencies: In rare cases, individuals may be born with a genetic inability to produce enough C3, leaving them vulnerable to recurrent and severe bacterial infections.
Severe Liver Disease: As the liver is the primary site of C3 production, significant liver damage can impair its ability to make the protein.
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
While high levels indicate production, low levels of C3 (hypocomplementaemia) often suggest that the complement system is being used up faster than it can be replaced. This 'consumption' is a key indicator that the immune system is engaged in a prolonged battle.
The most common causes of low C3 are autoimmune diseases. In conditions like Systemic Lupus Erythematosus (SLE), the complement system is mistakenly activated and directed against the body's own cells and tissues, leading to a continuous drain on C3 levels. A low C3 in someone with lupus can signal a disease flare-up, particularly involving the kidneys.
Other causes of low C3 include:
Chronic Infections: Persistent infections can lead to ongoing complement consumption.
Genetic Deficiencies: In rare cases, individuals may be born with a genetic inability to produce enough C3, leaving them vulnerable to recurrent and severe bacterial infections.
Severe Liver Disease: As the liver is the primary site of C3 production, significant liver damage can impair its ability to make the protein.
Low C3 Levels: A Sign of Immune Exhaustion or Deficiency
While high levels indicate production, low levels of C3 (hypocomplementaemia) often suggest that the complement system is being used up faster than it can be replaced. This 'consumption' is a key indicator that the immune system is engaged in a prolonged battle.
The most common causes of low C3 are autoimmune diseases. In conditions like Systemic Lupus Erythematosus (SLE), the complement system is mistakenly activated and directed against the body's own cells and tissues, leading to a continuous drain on C3 levels. A low C3 in someone with lupus can signal a disease flare-up, particularly involving the kidneys.
Other causes of low C3 include:
Chronic Infections: Persistent infections can lead to ongoing complement consumption.
Genetic Deficiencies: In rare cases, individuals may be born with a genetic inability to produce enough C3, leaving them vulnerable to recurrent and severe bacterial infections.
Severe Liver Disease: As the liver is the primary site of C3 production, significant liver damage can impair its ability to make the protein.
C3's Role Beyond Infection: Autoimmunity and Kidney Health
The complement system is a double-edged sword. While essential for fighting infection, its misdirection can cause significant damage. In autoimmune diseases, C3 plays a central role in the tissue injury that characterises these conditions.
This is particularly evident in certain types of kidney disease. In conditions like lupus nephritis or membranoproliferative glomerulonephritis (MPGN), complexes of antibodies and antigens are deposited in the delicate filtering units of the kidneys (the glomeruli). These deposits activate C3, triggering an inflammatory cascade that damages the kidneys and impairs their function. For this reason, measuring C3 is a routine part of monitoring disease activity in patients with these conditions.
C3's Role Beyond Infection: Autoimmunity and Kidney Health
The complement system is a double-edged sword. While essential for fighting infection, its misdirection can cause significant damage. In autoimmune diseases, C3 plays a central role in the tissue injury that characterises these conditions.
This is particularly evident in certain types of kidney disease. In conditions like lupus nephritis or membranoproliferative glomerulonephritis (MPGN), complexes of antibodies and antigens are deposited in the delicate filtering units of the kidneys (the glomeruli). These deposits activate C3, triggering an inflammatory cascade that damages the kidneys and impairs their function. For this reason, measuring C3 is a routine part of monitoring disease activity in patients with these conditions.
C3's Role Beyond Infection: Autoimmunity and Kidney Health
The complement system is a double-edged sword. While essential for fighting infection, its misdirection can cause significant damage. In autoimmune diseases, C3 plays a central role in the tissue injury that characterises these conditions.
This is particularly evident in certain types of kidney disease. In conditions like lupus nephritis or membranoproliferative glomerulonephritis (MPGN), complexes of antibodies and antigens are deposited in the delicate filtering units of the kidneys (the glomeruli). These deposits activate C3, triggering an inflammatory cascade that damages the kidneys and impairs their function. For this reason, measuring C3 is a routine part of monitoring disease activity in patients with these conditions.
Understanding Your Results
A C3 level is measured with a simple blood test. It is often ordered along with a Complement C4 test, as the ratio between the two can provide further diagnostic clues.
Complement C3 reference ranges are age-related and measured in grams per litre (g/L), as below:
Ages 0-40 Normal Range: 0.8-1.6 g/L
Aged 40+ Normal Range: 0.9-1.7 g/L
Some important notes:
Clinical correlation: Doctors interpret C3 results alongside symptoms, physical examination, and other laboratory tests, particularly C4 levels and other complement components.
Disease monitoring: In people with known autoimmune diseases, C3 levels help monitor disease activity and treatment response, with low levels often indicating active disease.
Complement function: C3 levels alone don't indicate complement system function, so doctors may order additional tests like CH50 (total complement activity) for complete assessment.
Repeat testing: C3 levels can fluctuate with disease activity and treatment, so periodic monitoring helps track immune system status over time.
Understanding Your Results
A C3 level is measured with a simple blood test. It is often ordered along with a Complement C4 test, as the ratio between the two can provide further diagnostic clues.
Complement C3 reference ranges are age-related and measured in grams per litre (g/L), as below:
Ages 0-40 Normal Range: 0.8-1.6 g/L
Aged 40+ Normal Range: 0.9-1.7 g/L
Some important notes:
Clinical correlation: Doctors interpret C3 results alongside symptoms, physical examination, and other laboratory tests, particularly C4 levels and other complement components.
Disease monitoring: In people with known autoimmune diseases, C3 levels help monitor disease activity and treatment response, with low levels often indicating active disease.
Complement function: C3 levels alone don't indicate complement system function, so doctors may order additional tests like CH50 (total complement activity) for complete assessment.
Repeat testing: C3 levels can fluctuate with disease activity and treatment, so periodic monitoring helps track immune system status over time.
Understanding Your Results
A C3 level is measured with a simple blood test. It is often ordered along with a Complement C4 test, as the ratio between the two can provide further diagnostic clues.
Complement C3 reference ranges are age-related and measured in grams per litre (g/L), as below:
Ages 0-40 Normal Range: 0.8-1.6 g/L
Aged 40+ Normal Range: 0.9-1.7 g/L
Some important notes:
Clinical correlation: Doctors interpret C3 results alongside symptoms, physical examination, and other laboratory tests, particularly C4 levels and other complement components.
Disease monitoring: In people with known autoimmune diseases, C3 levels help monitor disease activity and treatment response, with low levels often indicating active disease.
Complement function: C3 levels alone don't indicate complement system function, so doctors may order additional tests like CH50 (total complement activity) for complete assessment.
Repeat testing: C3 levels can fluctuate with disease activity and treatment, so periodic monitoring helps track immune system status over time.
The Takeaway
C3 serves as a vital component of your immune system's complement cascade, helping fight infections and maintain immune balance. Abnormal levels—either high or low—provide valuable clues about acute inflammation, chronic disease, or immune deficiency.
Understanding C3 helps you appreciate the complexity of your immune system and why doctors use complement testing alongside other assessments to diagnose and monitor immune-related conditions.
Don't ignore symptoms that might suggest immune system problems, such as recurrent infections, joint pain, or kidney problems, especially if accompanied by abnormal C3 levels, as early detection and treatment can prevent complications.
The Takeaway
C3 serves as a vital component of your immune system's complement cascade, helping fight infections and maintain immune balance. Abnormal levels—either high or low—provide valuable clues about acute inflammation, chronic disease, or immune deficiency.
Understanding C3 helps you appreciate the complexity of your immune system and why doctors use complement testing alongside other assessments to diagnose and monitor immune-related conditions.
Don't ignore symptoms that might suggest immune system problems, such as recurrent infections, joint pain, or kidney problems, especially if accompanied by abnormal C3 levels, as early detection and treatment can prevent complications.
The Takeaway
C3 serves as a vital component of your immune system's complement cascade, helping fight infections and maintain immune balance. Abnormal levels—either high or low—provide valuable clues about acute inflammation, chronic disease, or immune deficiency.
Understanding C3 helps you appreciate the complexity of your immune system and why doctors use complement testing alongside other assessments to diagnose and monitor immune-related conditions.
Don't ignore symptoms that might suggest immune system problems, such as recurrent infections, joint pain, or kidney problems, especially if accompanied by abnormal C3 levels, as early detection and treatment can prevent complications.
References
British Society for Immunology. (2020). Complement system disorders: diagnosis and management. Clinical Immunology Guidelines.
NHS. (2023). Lupus (systemic lupus erythematosus).
Sjoberg, A. P., Trouw, L. A., & Blom, A. M. (2009). Complement activation and inhibition: a delicate balance. Trends in immunology, 30(2), 83–90.
References
British Society for Immunology. (2020). Complement system disorders: diagnosis and management. Clinical Immunology Guidelines.
NHS. (2023). Lupus (systemic lupus erythematosus).
Sjoberg, A. P., Trouw, L. A., & Blom, A. M. (2009). Complement activation and inhibition: a delicate balance. Trends in immunology, 30(2), 83–90.
References
British Society for Immunology. (2020). Complement system disorders: diagnosis and management. Clinical Immunology Guidelines.
NHS. (2023). Lupus (systemic lupus erythematosus).
Sjoberg, A. P., Trouw, L. A., & Blom, A. M. (2009). Complement activation and inhibition: a delicate balance. Trends in immunology, 30(2), 83–90.
Research articles
Research articles
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