Coxiella Burnetii - IgG antibody, Serum

Bacterial/ Viral

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No Fasting Required

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Detects antibodies to Q fever agent.

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Coxiella Burnetii - IgG Antibody Serum Test Information Guide

Why is it done?
- Test Purpose: Detects IgG antibodies against Coxiella burnetii, the causative agent of Q fever (Query fever), a zoonotic infectious disease transmitted primarily through inhalation of contaminated aerosols from infected animals
- Primary Indications: Diagnosis of acute or chronic Q fever; suspected endocarditis in patients with Q fever exposure; investigation of fever of unknown origin in patients with potential animal contact; screening for Q fever in occupational exposure cases (veterinarians, farm workers, abattoir workers)
- Clinical Circumstances: Performed during acute infection phase or when chronic Q fever is suspected; typically ordered 2-3 weeks after symptom onset when antibody levels are detectable; may be repeated to assess for seroconversion or to evaluate progression from acute to chronic infection
Normal Range
- Reference Range: Negative or <1:64 (varies by laboratory methodology; results may be reported as negative, equivocal, or positive based on titer levels)
- Units of Measurement: Antibody titer (1:X dilution) or Index value (S/CO ratio - Signal to Cutoff); some laboratories report as qualitative (negative/positive) or quantitative (≥1:64 or ≥1:128 considered positive)
- Interpretation of Results: Negative (<1:64 or <1.0 Index): Absence of IgG antibodies; suggests no current or past Q fever infection, though early acute infection may be negative; Equivocal (Borderline): Requires repeat testing in 1-2 weeks to confirm seroconversion; may indicate early acute or resolving infection; Positive (≥1:64 or ≥1.0 Index): Indicates past or present infection; high titers (≥1:256) particularly suggestive of chronic Q fever or recently acute phase infection
- Normal vs. Abnormal: Normal (negative) = No evidence of Q fever exposure or infection; Abnormal (positive) = Evidence of Q fever infection at some point; clinical correlation with symptoms, IgM results, and Phase antigen status needed for interpretation
Interpretation
- Phase-Specific Interpretation: Phase I (Phase 1) Antibodies to Outer Membrane: Predominantly appear in chronic Q fever; high titers (≥1:256) suggest chronic infection especially with valvular involvement; Phase II (Phase 2) Antibodies to Lipopolysaccharide: Appear first in acute infection; presence without Phase I antibodies typically indicates acute Q fever
- Temporal Pattern of Antibodies: IgM antibodies appear first (within 7-10 days); IgG antibodies appear later (2-3 weeks post-infection); IgG persists long-term and indicates past or ongoing infection; rising titers between paired sera (acute and convalescent) confirm acute infection
- Diagnostic Patterns: Acute Q Fever: IgM positive, IgG II positive, IgG I negative or low; Chronic Q Fever (Q fever endocarditis): IgG I positive with high titers (≥1:256 to ≥1:1024), IgG II also positive; Past Infection: IgG positive, IgM negative; True Negative: All antibodies negative
- Factors Affecting Results: Timing of specimen collection relative to symptom onset; immunocompromised patients may have delayed or blunted antibody responses; antibiotic therapy (especially tetracyclines) can suppress antibody development if given early; previous Q fever vaccination affects baseline antibody levels; laboratory assay method variation (immunofluorescence, ELISA, complement fixation)
- Clinical Significance: Positive IgG with high Phase I titers is considered diagnostic for chronic Q fever (Q fever endocarditis) and warrants immediate evaluation for endocarditis, particularly in patients with pre-existing valvular disease; positive results in acute symptomatic phase supports acute Q fever diagnosis; negative results in acute phase don't exclude infection if within first 2 weeks of symptoms
Associated Organs
- Primary Organ Systems Involved: Respiratory system (lungs) - primary site of infection via inhalation; Cardiovascular system (heart valves) - target of chronic infection; Liver - hepatitis is common in acute Q fever; Bone marrow/Immune system - affects antibody production
- Associated Conditions: Acute Q Fever: Atypical pneumonia, hepatitis, fever of unknown origin, myalgia, arthralgia; Chronic Q Fever: Q fever endocarditis (infection of heart valves), prosthetic valve infection, vascular graft infections, osteomyelitis, vascular aneurysms
- Disease Associations: Q fever (Coxiella burnetii infection); Endocarditis (cardiac infection); Acute respiratory infection; Occupational zoonotic disease; Fever of unknown origin; Atypical pneumonia
- Potential Complications: Progressive endocarditis requiring valve replacement; septic emboli from infected valves to vital organs; heart failure from valvular dysfunction; acute renal failure; disseminated intravascular coagulation; hepatic dysfunction; chronic debilitating illness if untreated; mortality rate up to 5% in untreated chronic Q fever endocarditis
- High-Risk Populations: Patients with pre-existing valvular disease (rheumatic heart disease, prosthetic valves); immunocompromised individuals; pregnant women; patients on dialysis; those with previous cardiovascular surgery; occupational exposure groups
Follow-up Tests
- Primary Follow-up Testing: Coxiella burnetii IgG Phase I Antibody (specifically); Coxiella burnetii IgM Antibody (to assess acute phase); Paired acute and convalescent sera (obtain second sample 2-4 weeks after first to demonstrate seroconversion or rising titers)
- Cardiac Evaluation (if positive): Transthoracic echocardiography; Transesophageal echocardiography (TEE) for better visualization of valve abnormalities; Blood cultures (may be negative in Q fever endocarditis); ECG (evaluate for conduction abnormalities)
- Additional Diagnostic Testing: Polymerase Chain Reaction (PCR) for Coxiella burnetii DNA (particularly useful in acute phase or immunocompromised patients); Chest X-ray (evaluate for pneumonia); Liver function tests; Blood cultures; Complete blood count; ESR/C-reactive protein (inflammatory markers)
- Monitoring and Treatment Response: Repeat Q fever serology at 3-6 months intervals for chronic infection; assess antibody decline with treatment; IgG Phase I titers should decrease with appropriate long-term antibiotic therapy (typically 18-36 months); persistently elevated Phase I titers suggest inadequate treatment or ongoing infection
- Complementary Test Information: Other rickettsial serologies if differential diagnosis includes Rocky Mountain spotted fever, typhus, or other rickettsial diseases; Bartonella serology if endocarditis suspected; Fungal serology if disseminated infection suspected
Fasting Required?
- Fasting Status: NO - Fasting is not required for this serology test
- Patient Preparation: Patient may eat and drink normally prior to blood draw; no special dietary restrictions; can take regular medications as prescribed
- Specimen Collection Requirements: Serum sample required (typically 5-10 mL collected in SST or serum separator tube); allow blood to clot completely; do not use EDTA or other anticoagulants; refrigerate if transport is delayed; room temperature acceptable for short transport periods
- Timing Considerations: Test should be performed at least 2-3 weeks after symptom onset for optimal antibody detection; if negative during acute phase, repeat testing may be warranted; paired sera (acute and convalescent) collected 2-4 weeks apart provide better diagnostic accuracy
- Medication Considerations: No medications need to be withheld; continue all prescribed medications as normal; antibiotic therapy should not be delayed pending test results if Q fever is strongly suspected; early antibiotic treatment (doxycycline or tetracycline) may blunt antibody response if given very early in infection
- Additional Instructions: Inform healthcare provider of any Q fever exposure or occupational risk factors; document symptom onset date for accurate interpretation; provide information about animal contact or potential exposure sources; communicate if immunocompromised or on immunosuppressive therapy

How our test process works!