The reason for blood to be drawn during the pulmonary nodule review is to further assist in determining the nature of the nodule. Sometimes, CT imaging alone cannot accurately determine the benign and malignant nodules, because some pulmonary nodules may show imaging "camouflage" in the early stage, such as a stable and unchanged "cute" nodule on CT images, which may give us the illusion that "the years are quiet and the waves are calm". 
However, from a tumor biology point of view, this lesion may be hiding "choppy" changes under the iceberg. It may have developed a tendency to malignant transformation, or even metastasis of the lesion has occurred. Therefore, in order to assess the nature of the nodule more thoroughly, the results of blood tests need to be combined in addition to CT imaging.
For example, a blood test for antibodies, that is, a blood test for seven antibodies for lung cancer, can help us understand the activity of the nodule from a biological point of view, and then determine the nature of the nodule. Another obvious benefit of this technology is that it is safer than CT, there is no radiation, and only 2ml of blood is drawn.
Therefore, CT and blood tests are two very important tests for the follow-up of pulmonary nodules, which complement each other and are indispensable. By comprehensively analyzing the results of the two, the nature of the nodule can be assessed more accurately, providing more accurate guidance for the patient's ** and prognosis.