Description of the blood test:
The Bartonella henselae IgG test is a serological study designed to detect class G immunoglobulins against the causative agent of Cat Scratch Disease (CSD). While IgM antibodies signal the very beginning of an infection, IgG antibodies develop slightly later—typically reaching detectable levels 2 to 4 weeks after exposure. These antibodies represent the immune system’s long-term response and memory. This test is essential for confirming a diagnosis in the later stages of the illness, identifying chronic forms of bartonellosis, and determining if a patient has had a prior infection in the past.
What does the analysis represent?
- Immune Memory: A positive result indicates that the body has recognized and responded to the Bartonella bacterium.
- Late-Stage Detection: IgG is often more reliable than IgM for patients who have had symptoms (like swollen lymph nodes) for more than a month.
- Chronic & Atypical Forms: Used to investigate persistent fevers of unknown origin or systemic complications affecting the heart (endocarditis) or eyes (neuroretinitis).
- Performance: Indirect Fluorescent Antibody (IFA) or ELISA performed on a venous blood sample.
Recommendations for the test (General)
- Time: It is recommended to have blood drawn in the morning.
- Fasting: A food intake pause of 4–8 hours is advised for optimal sample quality.
- Clinical History: Provide details about any contact with cats, the presence of skin lesions, or how long your lymph nodes have been enlarged.
- Important: A single positive IgG result may only indicate a past infection. To diagnose a current active infection, doctors often look for a “fourfold increase” in the IgG titer between two samples taken 2–4 weeks apart.
What can affect the results?
- Persistence: IgG antibodies can remain positive for up to a year or more after the infection has cleared, which may complicate the diagnosis of a new, unrelated illness.
- Cross-reactivity: Results can be influenced by other infections, such as Bartonella quintana (transmitted by lice) or Coxiella burnetii.
- Severe Immunodeficiency: In patients with very weak immune systems, the body may fail to produce a significant IgG response despite a high bacterial load.
When to take the test?
- Recommendations: Prescribed for patients with subacute or chronic lymphadenopathy (swollen glands for more than 3 weeks), prolonged unexplained fever, or when initial IgM tests were negative but clinical suspicion remains high.
- Preparation: Standard preparation for venous blood work; no specific physical restrictions are required.
How to interpret the results?
The interpretation of data is the exclusive responsibility of an infectious disease specialist. A high IgG titer, especially when combined with typical symptoms, is a strong clinical marker for Bartonella infection. However, since many healthy cat owners have “background” antibodies, the results must be carefully correlated with the patient’s current health status. Only an expert can determine if the IgG levels signify a resolving acute case, a chronic condition requiring prolonged antibiotics, or simply a “serological scar” from a past encounter.
Possible further investigations
- Bartonella henselae IgM: To check for a concurrent acute immune response.
- Bartonella PCR: To detect the actual DNA of the bacteria, which is the most definitive way to confirm an active infection.
- Echocardiogram: If a heart murmur or systemic symptoms are present, to rule out Bartonella-related endocarditis.
- Consultation with an Infectious Disease Specialist: To evaluate the titer levels and establish a treatment plan.
When does the next step make sense?
If the IgG test is positive, it confirms that Bartonella has been or is currently active in your system. The next step is a consultation with a specialist to determine if your symptoms require treatment or if you have successfully developed immunity from a past exposure.
👉 If necessary, you can discuss the test results with our specialized — disease specialist Dermatologist (Doctors – TAMC).
