Human immunity comes from our own immune system, which is composed of immune organs, immune cells and immune factors. Immune cells and immune factors are distributed throughout the body and form a network of mutual constraints, which dominate the immune function of the body to resist invasion of bacteria and viruses, remove damaged degenerated and aging cells in the body, remove metabolic waste in the body, and maintain the stability of the internal environment of the body. What are the tests we need to do when we go to the hospital because of the decline of human immunity, including the ability to fight infection? 1, blood gas analysis: blood gas analysis is a medical test used to determine whether there is an imbalance in the acid-base balance of the body and the degree of hypoxia and hypoxia, plays a vital role in the treatment of acute respiratory failure, surgery and other processes. 2, urine specific gravity: urine specific gravity is the ratio of the weight of the same volume of water at 4 degrees Celsius, is an indicator of the concentration of solutes contained in urine. It is used to estimate the concentration function of the kidney, but the accuracy is poor and is affected by many factors. 3.Electrocardiogram: It is a technique that uses an electrocardiogram machine to record from the body surface a graph of the changes in electrical activity generated by each cardiac cycle of the heart. ECG is the best way to measure and diagnose abnormal heart rhythm. 4.Central venous pressure: It is the pressure at the upper and lower vena cava into the right atrium, measured through the upper and lower vena cava or the built-in tube of the right atrium. Usually the blood pressure of the right atrium and the large intra-thoracic veins is called the central venous pressure. 5.Average arterial pressure: It is the average value of arterial blood pressure in one cardiac cycle called average arterial pressure. The normal value of mean arterial pressure in normal adults is 70-105mmHg.