What are the other Names for this Test? (Equivalent Terms)
- Bordetella Pertussis Antibodies Test
- Bordetella Pertussis by DFA (Direct Fluorescent Antibody)
- Whooping Cough Test
What is Pertussis Test? (Background Information)
- Pertussis or whooping cough is a disease caused by bacterium Bordetella pertussis. A test for pertussis helps in diagnosing the infection
- Bordetella pertussis is transmitted from one individual to another via respiratory droplets. In individuals, who have been infected, the disease passes through 3-stages after an initial incubation period:
- The first stage (catarrhal stage) resembles a common cold
- The second stage (paroxysmal stage) involves sudden, severe bouts of coughing (and possibly a sharp intake of breath in between the coughing paroxysms, manifesting as a “whoop”)
- In the third stage (convalescent stage), the symptoms subside
Pertussis Testing may be conducted on a specimen sample obtained by swabbing the nasopharynx (part of the respiratory tract behind the nose) or on a sample of blood. The tests that may be performed include the following:
- Culture: It is done on a sample obtained from the nasopharynx. The specimen is placed on a nutrient medium, in order to allow the bacteria to grow and these are identified. Culture is the gold standard test to identify pertussis infection and results are reported in about 2 weeks
- Polymerase chain reaction (PCR): This test is also done on the nasopharyngeal specimen. The genetic material of the bacterium is amplified (increased in number) and subsequently identified, to make a diagnosis of pertussis. The results can be reported in a couple of days
- Direct fluorescent antibody (DFA): This test is less favored, compared to culture or PCR and may be used to identify bacteria grown in culture
- Pertussis antibodies: This test is performed on a blood sample and looks for the presence of antibodies (proteins produced by the immune system in response to infection) to Bordetella pertussis
What are the Clinical Indications for performing the Pertussis Test?
A Pertussis Test may be ordered to diagnose individuals suspected of having whooping cough or pertussis. Symptoms of the disease vary, depending on the stage at presentation and may include:
- Sneezing, fever, running nose (in the catarrhal stage)
- Sudden bouts of coughing (in the paroxysmal stage)
Later in the course of the disease, culture and PCR may be negative for infection and a blood test for antibodies is preferred.
How is the Specimen Collected for Pertussis Test?
Sample required: Nasopharyngeal swab/nasal aspirate/blood
- Nasopharyngeal swab is obtained by using a Dacron swab on a long thin stick. After tilting the head back, the swab is slowly introduced via a nostril, until it touches the nasopharynx and resistance is met. It is rotated gently to collect cell samples and withdrawn within a few seconds
- To get a nasal aspirate, a syringe is used to introduce a small amount of sterile saline into the nose, which is then gently suctioned out
- A blood sample is drawn via a needle, introduced into a vein in the arm
Preparation required: None
What is the Significance of the Pertussis Test Result?
The test outcomes and their significance are as follows:
- Culture: A positive result indicates Bordetella pertussis infection. A negative test does not rule out the disease, as the time of testing, the prior use of antibiotics, sample collection and transport, influence test outcomes
- PCR: A positive result indicates the likelihood of whooping cough, but other bacterial species of Bordetella may give positive results as well. A negative result does not conclusively rule out an infection
- Direct fluorescent antibody: A positive result, when conducted on a nasopharyngeal swab sample, indicates a likely infection. However, the test is less sensitive (ability of the test to pick out those infected) and less specific (ability of the test to pick out individuals, who do not have the disease) compared to a culture/PCR
- Antibody tests: The presence of IgM and IgA antibodies in the blood indicates a recent infection; the presence of IgG indicates infection or post vaccination status
The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.
Additional and Relevant Useful Information:
- Culture and PCR tests are less likely to be positive in the late stages of infection
The following article link will help you understand Pertussis.
Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.
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References and Information Sources used for the Article:
http://labtestsonline.org/understanding/analytes/pertussis/ (accessed on 03/15/2014)