Most rheumatologic diseases are systemic, meaning that they tend to affect multiple organs throughout the body and are often difficult to feel. Therefore, various tests are often used to accurately understand their presence and severity. Because the kidneys are more susceptible to damage from rheumatic and immune diseases, both physicians and patients attach importance to the examination of “kidney function” in clinical practice. Among them, blood creatinine and urea nitrogen are the most commonly used tests. However, the biggest limitation of these two items is that they cannot detect the damage of kidney function at an early stage. For example, blood creatinine will only increase when the kidney function is reduced to below 50-60%. In other words, by the time the creatinine is found to be elevated, the actual function of the kidney may have less than half left (half of the kidney function is barely enough, and any further decrease is not). Therefore, our main task is to treat kidney damage as early as possible once it occurs, and give treatment before creatinine rises, instead of waiting until creatinine rises to mend the situation. How to detect kidney damage early? There are several types of methods: blood test, urine test, kidney biopsy, kidney ultrasound, etc. Blood test includes not only creatinine but also serum cystatin measurement. Urine tests include accurate quantification of protein and analysis of protein composition (not simply how many + signs), urine red blood cell levels, etc., in addition to urine routine. Kidney biopsy is safe, easy to perform, less damaging, and not too expensive, usually around $3,000 before and after, and can provide a lot of valuable information, which is important for the long-term management of the disease. It must be performed in a unit with adequate experience. Renal ultrasound has some complementary value.