weil felix test

Rickettsia test

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clinical definition of weil felix test

The Weil-Felix test detects typhus and specific rickettsial infections. Rickettsia is bacteria transmitted by ticks, fleas, lice and is the root of diseases in human beings. Rickettsial disease comprises of a set of diseases caused by the microorganisms like typhus, rickettsialpox, Boutonneuse fever, African tick bite fever, Rocky Mountain spotted fever, Australian Tick Typhus, Flinders Island Spotted Fever, Queensland tick typhus, Q fever, southern tick-associated rash illness (STARI), ehrlichiosis, and tularemia. The Weil Felix treatment would depend upon the nature and severity of the infection.


what is weil felix test?

Diagnosis of Rickettsia is done with the help of an agglutination test, Weil Felix. Over the years it has been one of the most extensively used diagnostic procedure for detecting the infection. The basis of the Weil Felix test positive is to detect the anti-rickettsial antibodies present in the patient’s serum sample.


when do you expect results?

24 to 36 Hours


why get tested?

The Weil Felix test assesses the existence of rickettsia and varieties of rickettsial disease without specifications of species.


reason to take weil felix test test

Some of the initial Weil Felix symptoms include: 

• Lack of appetite, Headache

• Backache, Fever

• Nausea

• Vomiting

• A severe headache

• Muscle pain

• Swelling of the parotid glands (behind the ear) Later signs and symptoms include:

• Abdominal pain

Joint pain Skin Lesions

• Maculopapular rash

• Petechial rashes


preparations needed for weil felix test test

Preparatory instructions before the test *include:

No Fasting Required. No other special preparations required.


sample required?

Specimen type: Serum (Blood Sample),

Specimen collection procedure: Venipuncture - Collection of blood from a vein, usually from the arm.


what do my test results mean?

The below table helps in understanding the Widal Weil Felix test interpretation. A titer of ≥1:320 is considered positive. The result is interpreted with respect to the most dilute tube in the series that shows positive signs.

The results of the Weil Felix test report depend on the agglutination reactions occurring based on the antigens common to both organisms. This reaction validates the presence and type f rickettsial infection.


what is the basis of the weil felix test?

To understand what is Weil Felix test it is necessary to have an idea of the basis on the which the test is conducted. An antigenic cross reaction activity between few serotypes of Proteus spp (non-motile) and Rickettsia spp is considered as the Weil Felix test principle. The serum sample of the patient is screened for this Weil Felix reaction. A cross-reaction between the OX antigens (OXK, OX 2 and OX 19) Proteus species strains along with the antibodies produced in acute rickettsial infections forms the basis for the Weil Felix test interpretation.


how is the test done?

The procedure involves the collection of the blood sample from the patient in the tube or the vial and sending it for analysis. There are two methods of conducting the analysis at the lab.

Slide Method: A diminutive amount of the serum sample from the patient is placed on the slide after which the preferred antigen drop is added to it. The next step is to rotate the consequential postponement for a minute. If this results in visible agglutination, then a positive result is indicated.

Tube Method: As per the method twofold dilution of the serum sample is added to the tubes along with diluents, 0.25% of phenol saline. The tube’s final volume has to be made up to 1 ml. Antigen deferment is then further added and incubated for four to six hours at 50 to 55 °C. Positive results are indicated if there is granulation or visible flocculation.


does the test pose any risk?

There are no significant risks associated with the test. It is a simple blood test rarely a person might suffer from bruising or infection at the puncture site. The symptoms tend to gradually go away in some time.


what might affect my test results?

Consuming alcohol before the test or taking any over the counter medication might alter your test results. It is always advisable to inform your doctor if you are on any prescribed medication.


what other tests might i have along with this test?

The Weil Felix can serve as an initial screening test for rickettsia. Since the test does not provide any conclusive evidence, other tests like ELISA or immunofluorescence or Western blot are also prescribed by the doctor.


Understanding results ofWeil Felix Test

Reference RangeInterpretation
Slide or Tube Test: Titer of ? 1: 320Positive

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’


The Weil Felix test can be an important diagnostic tool in screening for typhus and various other rickettsial infections. The Weil Felix test positive treatment would depend on the type of infection.