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Test ID: ASPBA    
Aspergillus Antigen, Bronchoalveolar Lavage

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

As an aid in the diagnosis of invasive aspergillosis and assessing response to therapy

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

Invasive aspergillosis (IA) is a severe infection that occurs in patients with prolonged neutropenia following transplantation or in conjunction with aggressive immunosuppressive regimens (eg, prolonged corticosteroid use, chemotherapy). The incidence of IA is reported to vary from 5% to 20% depending on the patient population. IA has an extremely high mortality rate of 50% to 80%, due in part to the rapid progression of the infection (ie, 1-2 weeks from onset to death). Approximately 30% of cases remain undiagnosed and untreated at death.

 

Definitive diagnosis of IA requires histopathological evidence of deep-tissue invasion or a positive culture. However, this evidence is often difficult to obtain due to the critically ill nature of the patient and the fact that severe thrombocytopenia often precludes the use of invasive procedures to obtain a quality specimen. The sensitivity of culture in this setting also is low, reportedly ranging from 30% to 60% for bronchoalveolar lavage (BAL) fluid. Accordingly, the diagnosis is often based on nonspecific clinical symptoms (unexplained fever, cough, chest pain, dyspnea) in conjunction with radiologic evidence (computed tomography [CT] scan), and a definitive diagnosis is often not established before fungal proliferation becomes overwhelming and refractory to therapy.

 

Recently, a serologic assay was approved by the FDA for the detection of galactomannan, a molecule found in the cell wall of Aspergillus species. Serum galactomannan (Aspergillus antigen) can often be detected a mean of 7 to 14 days before other diagnostic clues become apparent, and monitoring of Aspergillus antigen can potentially allow initiation of preemptive antifungal therapy before life-threatening infection occurs.

 

The clinical utility of Aspergillus antigen testing in BAL specimens as an early prognostic indicator of IA has recently been assessed. These studies demonstrated equivalent or higher sensitivity compared to detection of Aspergillus antigen in serum.(1-4) This assay may be useful in the assessment of therapeutic response as antigen levels typically decline in response to effective antimicrobial therapy.

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.

<0.5 Index

Interpretation Provides information to assist in interpretation of the test results

A positive result in bronchoalveolar lavage (BAL) fluid supports a diagnosis of invasive, pulmonary aspergillosis. Positive results should be considered in conjunction with other diagnostic procedures, such as microbiologic culture, histological examination of biopsy specimens, and radiographic evidence (see Cautions).

 

A negative result in BAL fluid does not rule out the diagnosis of invasive aspergillosis (IA). Patients at risk of IA should be monitored twice a week for Aspergillus antigen levels in serum until determined to be clinically unnecessary.

 

Aspergillus antigen levels typically decline in response to effective antimicrobial therapy.

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

False-positive results are reported to occur at rates of 8% to 14% with this assay when performed on serum. Numerous foods (pasta, rice, etc) contain galactomannan. It is thought that damage to the gut wall by cytotoxic therapy, irradiation, or graft-versus-host disease enables translocation of the galactomannan from the gut lumen into the blood and may be partially responsible for the high false-positive rate of this assay when serum is tested. Whether false-positive results in bronchoalveolar lavage (BAL) fluid are associated with the consumption of certain foods, as is observed in serum samples, remains to be determined.

 

Other genera of fungi such as Penicillium and Paecilomyces have shown reactivity with the rat EBA-2 monoclonal antibody used in the assay. These species are rarely implicated in invasive fungal disease. Specimens containing Histoplasma antigen may cross-react in the Aspergillus antigen assay. Cross-reactivity with Alternaria species also has been reported.

 

Semisynthetic antibiotics such as piperacillin, amoxicillin, and Augmentin, which are based on natural compounds derived from the genus Penicillium, have been demonstrated to cross-react with the rat EBA-2 monoclonal antibody used in the assay.

 

The specificity of the assay for Aspergillus species cannot exclude the involvement of other fungal pathogens with similar clinical presentations such as Fusarium, Alternaria, and Mucorales.

 

The performance of the assay has not been evaluated other specimen types such as urine or cerebrospinal fluid.

 

The assay may exhibit reduced detection of Aspergillus antigen in patients with chronic granulomatous disease and Job's syndrome.

 

The concomitant use of antifungal therapy in some patients with invasive aspergillosis may result in reduced sensitivity of the assay.

 

False-positive results are possible in patients receiving PLASMA-LYTE for intravenous hydration or if PLASMA-LYTE is used during bronchoscopy for the collection of BAL fluid.

Supportive Data

In clinical studies submitted to the FDA, the sensitivity of the test for serum was reported to be 81% for proven/probable invasive aspergillosis (n=31 patients), and the specificity was 89% (n=148 patients). The positive and negative predictive values were reported as 68% and 96% respectively, based on an average prevalence of 14% in the study population. In a low prevalence population (5%), the positive predictive value decreases to 31%; the negative predictive value remains at 96%.(Package insert: Platelia Aspergillus EIA, Bio-Rad, Redmond, WA, 6/2003).

 

Accuracy:

The performance characteristics of the Platelia Aspergillus EIA for the detection of galactomannan in BAL fluid were validated at Mayo Medical Laboratories by comparison of results obtained from an outside reference laboratory using the same assay. These studies demonstrated 95.6% (240/251) agreement between sites (Table 1).

 

 

Table 1: Comparison of Platelia Aspergillus Antigen results at Mayo Medical Laboratories and an Outside Reference Laboratory using BAL fluid (n=251).

 

Outside Reference Lab Aspergillus Antigen Result

MML Aspergillus Antigen Result

Positive

Negative

Positive

24

    1

Negative

10

216

Percent Agreement: 95.6% (240/251) (95% confidence interval; 92.2-97.6)

Kappa value: 0.79

 

For 10 of the 11 discordant results, testing at Mayo Medical Laboratories correlated with either serum Aspergillus antigen levels or fungal culture.  

 

Precision:

Intra- and inter-assay precision was tested for negative, mid-range and high-positive, spiked bronchoalveolar lavage (BAL) specimens. The mean index values, standard deviation and percent coefficient of variation were all acceptable, indicating excellent precision. (Table 2-3)

 

Table 2: Intra-assay precision studies

 

Mean Index

Standard Deviation

% Coefficient of Variation

Negative

0.23

0.05

22.1

Mid-Positive

2.23

0.16

  6.9

High Positive

4.29

0.43

  9.9

Positive: >0.5

Negative: <0.5

 

Table 3: Inter-assay precision studies

 

Mean Index

Standard Deviation

% Coefficient of Variation

Negative

0.20

0.05

25.5

Mid-Positive

2.32

0.39

17.1

High Positive

4.45

0.84

18.9

Positive: >0.5

Negative: <0.5

 

Analytical Specificity:

Cross-reactivity studies were performed by testing analyte-negative BAL specimens that had been spiked with varying concentrations of positive control material for the following organisms: Histoplasma capsulatum, Blastomyces dermatitidis, or Cryptococcus neoformans. These studies demonstrated that high concentrations of Histoplasma and Blastomyces antigen in BAL may yield positive results by the Platelia Aspergillus antigen assay. This has been demonstrated in prior published studies (5), and is a known limitation of this test that there may be cross-reactivity with dimorphic fungal pathogens.

 

In addition to the studies above, an analyte-negative BAL specimen was spiked with a pleural fluid that was known to be positive for Streptococcus pneumoniae antigen. This spiked-specimen was tested by the Platelia assay and was negative at all dilutions tested.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Park SY, Lee S, Choi S, et al: Aspergillus galactomannan antigen assay in bronchoalveolar lavage fluid for diagnosis of invasive pulmonary aspergillosis. J Infect 2010;61:492-498

2. Husain S, Clancy CJ, Nguyen MH, et al: Performance characteristics of the Platelia aspergillus enzyme immunoassay for detection of Aspergillus galactomannan antigen in bronchoalveolar lavage fluid. Clin Vaccine Immunol 2008;15(12):1760-1763

3. Meersseman W, Lagrou K, Maertens J, et al: Galactomannan in bronchoalveolar lavage fluid a tool for diagnosing aspergillosis in intensive care unit patients. Am J Respir Crit Care Med 2008;177:27-34

4. Becker MJ, Lugtenburg EJ, Cornelissen JJ, et al: Galactomannan detection in computerized tomography-based bronchoalveolar lavage fluid and serum in haematological patients at risk for invasive pulmonary aspergillosis. Br J haematol 2003;121:448-457

5. Xavier MO, Pasqualotto AC, Cardoso IC, Severo LC. Cross-reactivity of Paracoccidioides brasiliensis, Histoplasma capsulatum, and Cryptococcus species in the commercial Platelia Aspergillus enzyme immunoassay. Clin Vaccine Immunol 2009 Jan;16(1):132-133