If a patient has low albumin, it can cause swelling. The albumin in the blood vessels mainly maintains the colloid osmotic pressure in the blood. When the protein is low, the colloid osmotic pressure of the blood drops significantly, so that the fluid inside the blood vessels is lost outside the blood vessels, that is, in the third interstitial space of the body, resulting in edema, which can also appear as pleural effusion, peritoneal effusion, pericardial effusion, etc. The edema caused by low albumin is mostly generalized and concave, and is more obvious in low hanging areas, such as the lower extremities, lumbosacral area, etc.