Lung Function is Significantly Reduced From Asbestosis
A history of asbestos exposure may provide the first clue to the diagnosis of asbestos diseases such as asbestosis and asbestos pleural disease. It often takes decades between the patient's asbestos exposure and the appearance of early symptoms such as shortness of breath and chest pain.
A physician may test for asbestosis by using a stethoscope to listen for basal crackles or persistent high-pitched sounds that are characteristic of the disease. An x-ray may show small irregular opaque areas, usually in the lower lobes of the lungs. Pleural plaques indicative of asbestos pleural lung disease may also show up in an x-ray. However, x-rays are limited in detecting early asbestos disease, sometime yielding false positives for smokers as well as false negatives.
Asbestosis is Often Detected Through CT Scans
A computed tomography or CT scan may be more useful in indicating asbestosis and asbestos-related pleural disease than the chest x-ray, particularly in those cases in which the chest x-ray is ambiguous or in asbestos-exposed patients who have normal chest x-rays. A CT scan is a radiographic technique that uses a computer to combine multiple x-ray images into a two dimensional cross-sectional x-ray image. A machine rotates 180 degrees around the patient's body, sending out a thin x-ray beam at numerous points. Crystals at the opposite points of the beam pick up and record the absorption rates of the varying thickness' of tissue and bone. The computer turns the information into a detailed picture.
A high resolution CT scan (HRCT or "thin-slice" scan) can be even more accurate than a conventional CT scan. HRCT differs from the conventional CT in that it uses a very narrow x-ray beam (1-1.3mm slice thickness compared to conventional 8-10mm) and a high spatial frequency reconstruction to provide extremely high definition images of the lungs (High Resolution CT of the Lung, Radiology Update).
When only asbestos-related pleural disease is found using an x-ray or CT scan for diagnosis, it is not uncommon to later find pathologic evidence of asbestosis that was undetectable except on biopsy or autopsy. Some researchers feel that it is this sub-radiographic asbestosis which explains symptoms and pulmonary function abnormalities in individuals with evidence of only asbestos-related pleural disease, while others feel it is the impact of the pleural scarring on breathing mechanics which accounts for these findings.
Asbestosis and Lowered Lung Capacity
Pulmonary function tests (PFT) are breathing tests used to measure lung capacity and lung and chest wall mechanics. One method is to have the patient breath through a tube connected to a recording machine, taking a deep breath in and blowing out as quickly as possible. The results are recorded and analyzed.
Measurements include the amount of air the lungs can hold (total lung capacity), how quickly air is moved in and out of the lung, and how well the lungs can transfer oxygen from the air into the blood. As the lungs become scarred, these functions are reduced.
Asbestosis Diagnosis: Biopsies
Sometimes the patient's x-ray or CT scan shows a pulmonary nodule or lesion. The doctor may not be able to determine, based on the x-ray or CT alone, whether the nodule is cancerous. Because those with asbestosis or asbestos-related pleural disease have an increased chance of developing asbestos lung cancer or mesothelioma, a biopsy may be performed on the nodule. A biopsy is a surgical procedure in which a tissue specimen (in this case, the nodule) is sampled and examined under the microscope. Although a more invasive procedure than x-rays or CTs, the biopsy can provide invaluable medical information.