Lab testing

Diagnosing CPA

Samples of blood, sputum, tissue from a bronchoscopy, fluid from a lung (BAL fluid) and tests for general immune function and specific antibody levels are all processed in the Microbiology Lab initially.

Samples which are positive for fungus are then sent  for specialised testing relating to Aspergillus identification . These are all performed in the Mycology Reference Centre Manchester (MRCM) at UHSM.

This is a specialised laboratory which measures samples for a whole spectrum of tests relating to infection with Aspergillus species.  

A blood sample may be taken and sent to the laboratory to analyse whether antibodies to aspergillus are present in the blood or in a tissue fluid– this test may also be called an aspergillus precipitin test. A positive result means that antibodies to the fungus have been detected.

A positive test result is a useful marker for later comparisons to assess efficiency of treatment. However, false positive results do occur as all people are exposed to aspergillus in the air that they breathe.

A test for a particular fungal molecule sometimes found in the blood - called the galactomannan test may also be carried out on a blood sample and has proved a more reliable detection method for aspergillus presence, than testing for aspergillus antibodies alone.  Another way of detecting aspergillus is with a sensitive molecular testing method.

Sometimes markers of allergy to aspergillus are positive in the blood so specific IgE and IgG levels may be monitored.

A sample of sputum or other tissue fluids or tissue biopsies may be sent to the laboratory to be cultured to see if it is possible to grow aspergillus from the sample using a special culture plate, usually at the same time the sample is analysed by microscopy with specific stains to aid the identification of any aspergillus present.

In addition other general tests which may be undertaken include blood count, plasma viscosity and C-reactive protein which may indicate inflammation - such markers usually improve on treatment so a baseline level is helpful. Liver and kidney function tests are important as liver function can be abnormal on antifungal drugs.

Monitoring CPA progress 

Repeat blood tests for aspergillus precipitins are usual and once antifungal therapy is in place other tests for sensitivity are requested. The observation that some strains of  Aspergillus are resistant to itraconazole therapy, was first reported in 1997 in three clinical isolates from California obtained in the late 1980s; since then, a small number of clinical cases have been published. But the emergence of itraconazole resistance alone is of concern, and widespread azole cross-resistance would be devastating, particularly for oral treatment.  For CPA azole treatment with itraconazole, voriconazole and latterly posaconazole is the backbone of therapy with azoles being the only licensed class of oral drugs for aspergillosis. Studies in our local Mycology Laboratory have indicated that azole resistance is an emerging problem for the treatment of aspergillosis. Testing for drug sensitivity and resistance is one of the major tests undertaken on patient's blood samples to assure optimal drug dosing and detection of any resistance.

E Test. Test for sensitivity of Aspergillus to Itraconazole at different concentrations. In this case the Aspergillus was resistant to Itraconazole.	E Test for Aspergillus sensitivity to Voriconazole. In this example Aspergillus was sensitive to Voriconazole.

Other tests for immune levels and other lung disease

Some people with CPA don't have good immune protection against bacterial infections. Normally when a person meets a bacterium for the first time, they produce antibodies to that bacterium which help protect their body from infection. A common lung bacterium causing chest infections and pneumonia is Streptococcus pneumoniae, otherwise know as Pneumococcus- so pneumococcal antibodies will be tested for. Because pneumonia is common in children and older people there is a pneumococcal vaccine ('pneumonia jab'), which is commonly given to combat infection with the Pneumococcus bacteria. After the pneumonia jab, if blood tests show that antibodies are high, that  indicates good protection.

However in some people with CPA, the pneumococcal antibodies in their blood are very low. We can test this with a simple blood test. If the antibodies are low, then we will offer a pneumococcal vaccine (there are 2 types), and retest the blood a month or so later to see if antibody levels have gone up. If not, then sometimes the other pneumonia vaccine is given and may be more effective. The alternatives if the vaccine is not suitable are long term antibiotics, gamma interferon treatment or occasionally immunoglobulin replacement.

Also some aspergillosis patients may have low levels of a substance called mannose binding lectin (MBL) and display abnormal genes for this protein. This molecule may be tested for in a patient's blood and forms part of an ongoing research study to determine whether MBL can be used as a useful diagnostic aid.