Bronchoalveolar lavage fluid samples are sometimes evaluated. This uses a fiber optic bronchoscopy to obtain a small piece of lung tissue. This is a semi-invasive procedure. It is not reliable on dose, or prediction of disease. The sample can be tested for fibronectin, which is a mediator released by macrophages in the presence of asbestos. It can also be tested for procollagen III, where levels increase in those who are exposed. Scientists are also looking into testing for gene expressions of anti-oxidant enzymes, which are occur when asbestos is present. Studies are also looking into biomarkers in blood serum. Studies are pointing to elevated levels of the amino-terminal peptide of procollagen III found in exposed people. Studies are also looking at biomarkers in urine. It has been found that in asbestos workers, there is an increase in the excretion of the oxidative DNA adduct 8-hydroxy-deoxyquanosine, which indicates DNA damage