Stage four of diabetic nephropathy indicates the presence of significant amounts of urinary protein. At this stage, patients may exhibit symptoms of nephrotic syndrome, which means the total urinary protein quantification over 24 hours may exceed 3.5 grams, and the plasma albumin level may be lower than 30 grams per liter. Due to the large amount of protein leakage, patients may experience edema, presenting as swelling of the lower limbs or eyelids, or even severe generalized swelling. In addition to edema, patients may also have pleural and abdominal effusion, leading to pulmonary edema. Excessive fluid can overburden the heart, causing heart failure, which manifests as chest tightness, shortness of breath, and difficulty breathing, especially when the patient is active, these symptoms of chest tightness and shortness of breath become more pronounced.