Understanding Lab Tests for Infections
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Infections occur when harmful microorganisms such as bacteria, viruses, fungi, or parasites invade the body and multiply. While some infections can be diagnosed through specific pathogen detection, many infections are identified and monitored through blood tests that measure the body's immune response and inflammatory markers.
Top Recommended Test
Complete Blood Count / CBC (includes Differential and Platelets)
This fundamental test measures white blood cell count, which typically becomes elevated during infections as the immune system mobilizes to fight pathogens. The differential count can help distinguish between bacterial and viral infections.
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How Blood Tests Help Detect Infections
When the body fights an infection, it produces measurable changes in blood components including white blood cells, antibodies, and immune system proteins. These blood markers can reveal the presence of an infection, help determine its severity, and monitor the effectiveness of treatment.
Other Relevant Tests
IgG
This test measures immunoglobulin G antibodies, which are produced by the immune system. Elevated IgG levels can indicate chronic or past infections, as the body produces more of these antibodies to combat long-term infections.
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IgG, IgA, Indirect Immunofluorescence
This comprehensive immunofluorescence test detects specific antibodies against various infectious agents, helping to identify and diagnose specific infections by measuring the body's antibody response to particular pathogens.
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Antibody Screen, RBC with Reflex to Identification, Titer, and Antigen Typing
This test measures antibody concentration (titer) in the blood. High antibody titers can indicate an active ongoing infection, as the immune system produces increased levels of antibodies to combat invading pathogens.
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Complement Component C1q
This test measures C1q, a key component of the complement system that helps fight infections. Decreased C1q levels may be observed in severe infections, as this protein is consumed during the immune response against pathogens.
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Fibrinogen Antigen
This test measures fibrinogen, a protein that increases during inflammation and infection. Elevated levels can suggest an ongoing infectious process as part of the body's acute phase response to infection.
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Specialized Testing Considerations
Some individuals may require additional monitoring for infection risk, particularly those with compromised immune systems or those taking immunosuppressive medications. Regular blood testing helps ensure early detection of infections in these vulnerable populations.
Important Considerations
The information provided here is for educational purposes only and is not a substitute for professional medical advice. Blood test results must be interpreted by qualified healthcare providers who can correlate findings with clinical symptoms and medical history. Always consult with a healthcare provider for proper diagnosis and treatment of suspected infections.
