Test Catalog

Test ID: TULAB    
Francisella tularensis Antibody, IgM and IgG, ELISA, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Aiding in the diagnosis of tularemia caused by Francisella tularensis

 

These assays should not be used as a test of cure as they are not quantitative and patients may remain seropositive for months to years following resolution of disease.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Francisella tularensis is a small, intracellular, coccobacillary Gram negative bacterium and is an obligate pathogen in animals and humans, primarily maintained in rabbits, hares, cats, ticks and deerflies. F tularensis is found throughout North America and parts of Asia, and similar to Brucella species is considered a potential agent of bioterrorism. Human infection with F tularensis usually occurs through inhalation of infected aerosols, ingestion of contaminated meat or water, handling of diseased or sick animals, or through the bite of an infected arthropod (eg, tick, deerflies).

 

Following a 3 to 5 day incubation period, the clinical manifestations of infection with F tularensis differ primarily depending on the site and route of infection. The most common form of disease is ulceroglandular (45%-80% of cases), which is associated with an arthropod (or animal) bite or another cause of skin barrier compromise. This leads to development of a painful papule which ultimately ulcerates following which the bacterium enters the lymphatic system. Glandular tularemia is similar in presentation to ulceroglandular disease, however it lacks the ulceration and more frequently causes septicemia. Other, less frequent clinical manifestations include oculoglandular (Parinaud syndrome), oropharyngeal and gastrointestinal disease, pneumonic or typhoidal tularemia.

 

Diagnostic testing options for F tularensis primarily include culture and serology. Physicians suspecting tularemia should collect appropriate specimens (eg, skin lesion biopsy, lymph node aspirates, etc.) promptly and send for culture. The microbiology laboratory should be alerted to the possibility of F tularensis to ensure that appropriate safety measures are taken to protect the laboratory technologists. Growth on culture is a definitive means of making a diagnosis of tularensis. Serologic testing may be used to support a diagnosis of current or recent tularensis in patients who are IgM positive, or seroconvert to IgM, or IgG positive in paired sera collected 2 to 3 weeks apart.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Negative

Reference values apply to all ages.

Interpretation Provides information to assist in interpretation of the test results

IgM Result

IgG Result

Interpretation

Negative

Negative

No antibodies to Francisella tularensis detected. Antibody response may be negative in samples collected too soon following infection/exposure. Repeat testing on a new sample if clinically indicated.

Positive

Negative

IgM class antibodies to F tularensis detected, suggesting current or recent infection. Repeat testing in 2 to 3 weeks to detect seroconversion of IgG may be considered to confirm the diagnosis.

Positive

Borderline

Borderline

Negative

Questionable presence of IgM antibodies to F tularensis. Consider repeat testing in 1 to 2 weeks.

Borderline

Positive

IgG class antibodies to F tularensis detected suggesting recent or past infection. Clinical correlation alongside presentation, exposure history and other laboratory findings required.

Borderline

Borderline

Questionable presence of IgM and IgG class antibodies to F tularensis. Consider repeat testing in 1 to 2 weeks.

Positive

Positive

IgM and IgG class antibodies to F tularensis detected suggesting current, recent or past infection. Clinical correlation alongside presentation, exposure history and other laboratory findings required.

Negative

Positive

IgG class antibodies to F tularensis detected suggesting recent or past infection. Clinical correlation alongside presentation, exposure history and other laboratory findings required.

Negative

Borderline

Questionable presence of IgG antibodies to F tularensis. Consider repeat testing in 1 to 2 weeks.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

False negative results may occur in samples collected too soon following symptom onset, prior to the development of a detectable immune response. Repeat testing on new samples collected 2 to 4 weeks later may be helpful.

 

False positive results may occur in patients previously or currently infected with Brucella species. Other less frequent causes of cross-reactivity that have been reported include prior infection with Yersinia, Salmonella, or Legionella species.

 

IgM-class antibodies may be detectable as soon as 1 week after symptom onset and may remain detectable for multiple years following resolution of disease in some individuals. Therefore, an IgM positive result may not indicated current or recent infection in some cases.

 

There are multiple subspecies of Francisella tularensis, including F tularensis subspecies tularensis, F tularensis subspecies holarctica and F tularensis subspecies novicida, that are found throughout the norther hemisphere, including in the United States. The IgM and IgG anti-F tularensis ELISA tests used at Mayo Clinic Laboratories are based on the lipopolysaccharide (LPS) antigen of F tularensis. Although not directly tested, previous studies indicate that there are no antigenic differences between the LPS of F tularensis subspecies tularensis and the other subspecies. Therefore, these assays should not be used to differentiate between infection with the various F tularensis subspecies.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Petersen JM, Schriefer ME, Araj GE: Francisella and Brucella. In Manual of Clinical Microbiology. 12th Edition. 2019

2. Nigrovic LE, Wingerter SL: Tularemia. Infect Dis Clin North Am. 2008; 22(3): 489-504. doi: 10.1016/j.idc.2008.03.004