Cyanosis is a diffuse cyanosis of the skin and mucous membranes. It is usually most evident in areas with thin, less pigmented skin and adequate blood (e.g., lips, tongue, oral mucosa, tip of the nose, cheeks, earlobes, and nail beds). Examination for cyanosis should be performed in good natural light and may mask the presentation of cyanosis if there is significant skin pigmentation, jaundice, anemia, or puffiness. There are many clinical reasons for cyanosis (due to increased levels of reduced hemoglobin in the blood); the color of cyanotic skin may fade briefly with pressure (the color remains the same with pressure in abnormally pigmented skin). In a cold environment, cyanosis can also occur in healthy people due to vasoconstriction of the skin, so attention should be paid to differentiate it during the examination. In patients with cyanosis, attention should be paid to the time of cyanosis, the cause, accompanying symptoms, and signs (cardiopulmonary signs, peripheral circulation, pestle finger, etc.). What tests should be done for cyanosis? Fiberoptic bronchoscopy can directly observe the lesions of trachea and bronchus, and conduct corresponding examination and treatment according to the lesions. 2, skin test, skin test can reflect the actual immune status of the body’s combined effect of various factors, to understand whether the body is allergic to this substance. 3, residual air volume (RV), residual air volume (RV) test can understand the situation of lung function. 4.Oxygen saturation (SaO2), blood oxygen saturation (SaO2) has diagnostic significance for hypoxia.