Renal edema, or nephrogenic edema, has the following three main causes: 1. After the occurrence of kidney disease, the glomerular filtration rate decreases, resulting in water and sodium retention; 2. Because of the effect of renin angiotensin, which leads to increased permeability of the systemic capillaries, so that water in the blood vessels can more easily permeate into the tissue interstitium; 3. In patients with chronic kidney disease, the loss of urinary protein often leads to plasma albumin decreases, leading to a decrease in the colloid osmotic pressure of plasma, which allows water in the blood vessels to permeate into the tissue interstitium. These three causes are the main reasons for nephrogenic edema. Nephrogenic edema is a very common early symptom of kidney disease, so when edema is found, it is important to go to nephrology for diagnosis and differential diagnosis early.