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What is Aspergillus (Galactomannan) Antigen test?

Aspergillus is a fungus that is present in abundant amounts in the environment. Most of us inhale aspergillus spores with air without suffering from any negative effects. However, this fungus can cause infections or allergies in those who have a weak immune system. Cancer patients and people who have diseases such as asthma, emphysema, tuberculosis or cystic fibrosis are also prone to aspergillus infections.

Aspergillosis is the most common infection caused by aspergillus. It is a disease of the respiratory system caused by the growth of aspergillus inside the airway. The most severe form of aspergillosis is invasive aspergillosis. In this condition, the infection spreads to the blood vessels and tissues. If left untreated, invasive aspergillosis can lead to death.

If you get invasive aspergillosis, aspergillus will release a protein called galactomannan in your bloodstream. So, Aspergillus galactomannan antigen test is used to determine if you have invasive aspergillosis. 

(Read more: Aspergillus antibodies test)

  1. Why is an Aspergillus (Galactomannan) Antigen test performed?
  2. How do you prepare for Aspergillus (Galactomannan) Antigen test?
  3. How is Aspergillus (Galactomannan) Antigen test performed?
  4. What do Aspergillus (Galactomannan) Antigen test results mean?

Your doctor may order this test if you show symptoms of invasive aspergillosis. These symptoms depend on the organs that are affected, but the usual symptoms are as follows:

In severe cases, the following additional symptoms may be seen:

Ideally, the diagnosis of this disease should be done with a sample of the affected tissue. However, such samples are difficult to obtain due to the critical condition of the affected person.

On the other hand, isolating galactomannan from blood is less invasive. It also provides rapid results - within seven to 14 days - and can be beneficial in beginning the treatment early.

For people who are already being treated for invasive aspergillosis, this test helps in checking the therapeutic response. 

Foods, such as rice, and pasta contain galactomannan and must be avoided before this test.

Damage to the stomach wall - due to cytotoxic therapy, irradiation or graft-versus-host disease - may give false results.

Certain conditions such as chronic granulomatous disease and Job syndrome may also affect the test results.

So, discuss your food habits and medical history with your doctor before the test. He/she may ask you to make minor changes to your diet before the test.

Also inform your doctor if you are taking any medicine as certain drugs such as amoxicillin and piperacillin may affect the test results. 

This test may be performed on a blood sample or bronchoalveolar lavage fluid sample.

Blood test:

Your doctor would extract the required amount of blood from a vein in your arm. You may feel a bit of pain as the needle goes in - it’ll subside soon. After the test, you may feel lightheaded or dizzy for a while. It is also common to get a temporary bruise at the site of needle insertion. However, if any of the discomforts persist, please inform your doctor at the earliest.

Bronchoalveolar lavage:

In this procedure, a small sample of tissues is collected from the affected areas - in this case, lungs. Here is how the procedure is done 

  • A bronchoscope tube will be passed into the most affected region of your lungs.
  • An aliquot of 50 mL saline will be put into your lungs 
  • The doctor will wait for a few seconds and with constant pressure suck the fluid out till no more is present.
  • The procedure is repeated thrice and the sample will be sent to the lab for testing.

Normal results:

The test is negative in normal conditions. It indicates the absence of Aspergillus antigen in the body. For the test to be negative, the cut-off value should be less than 0.5 for serum and from 1-2 for bronchoalveolar lavage fluid. The doctor may order a repeat test for invasive aspergillosis if they suspect the infection. 

Abnormal results:

If the value is higher than the cut-off value, the test result is said to be positive. Positive results indicate that you have Aspergillus antigen in your body and hence invasive aspergillosis. This test should be considered along with other diagnostic tests such as histological exam of the biopsy sample, microbiological culture or radiographic evidence.

For all positive results, the test should be performed on another aliquot of the same sample, and a new sample should be collected for a follow-up test. Positive results from two or more consecutive tests from two separate samples can be used to confirm the diagnosis of invasive aspergillosis. 

In certain conditions, the test may give positive results, although Aspergillus may be absent. These conditions are as follows:

  • Consumption of antibiotics such as piperacillin/tazobactam and amoxicillin/sulbactam 
  • Consumption of certain drugs such as meropenem and cephalosporins
  • Consumption of foods such as pasta and yoghurt
  • In people with permeable small bowel, like mucositis after chemotherapy

Sometimes, the test results may be negative, although the infection is present. The conditions in which it may give false-negative results may be as follows:

  • Consumption of itraconazole and posaconazole, the antifungal drugs for prophylaxis
  • Galactomannan may not have developed yet as it is early in the infection

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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References

  1. American Thoracic Society [Internet]. NY (U.S.A). Aspergillosis Fungal Disease
  2. American Academy of Allergy, Asthma and Immunology [Internet]. Milwaukee (WI); Allergic Bronchopulmonary Aspergillosis (ABPA)
  3. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Aspergillosis
  4. Patterson TF. Practice Guidelines for the Diagnosis and Management of Aspergillosis: 2016 Update by the Infectious Diseases Society of America.. Clin Infect Dis. 2016 Aug 15;63(4):e1-e60. PMID: 27365388
  5. Ansorg R, van den Boom R, Rath P. Detection of Aspergillus galactomannan antigen in foods and antibiotics. Mycoses 1997 Dec;40(9-10):353-357. PMID: 9470421.
  6. Swanink CM, Meis JF, Rijs AJ, et al. Specificity of a sandwich enzyme-linked immunosorbent assay for detecting Aspergillus galactomannan. J Clin Microbiol 1997 Jan;35(1):257-260. PMID: 8968919.
  7. Pinel C, Fricker-Hidalgo H, Lebeau B, et al. Detection of circulating Aspergillus fumigatus galactomannan: value and limits of the Platelia test for diagnosing invasive aspergillosis. J Clin Microbiol 2003 May;41(5):2184-2186. PMID: 12734275.
  8. Maertens J, Verhaegen J, Lagrou K, et al. Screening for circulating galactomannan as a noninvasive diagnostic tool for invasive aspergillosis in prolonged neutropenic patients and stem cell transplantation recipients: a prospective evaluation. Blood 2001 March 15;97(6):1604-1610. PMID: 11238098.
  9. Aspergillus & Aspergillosis Website: Fungal Infection Trust. NHS National Aspergillosis Center. Manchester. U.K. Antigen testing
  10. University of Iowa. Department of Pathology. Laboratory Services Handbook [internet]. Aspergillus Galactomannan Antigen-Blood
  11. National Health Service [internet]. UK; Blood Tests
  12. Department of Medicine: Indiana University School of Medicine [Internet]. U.S.A. Bronchoalveolar Lavage Laboratory