There is a big difference between morning urine and second urine. Morning urine is urine that is excreted in the morning after waking up, before eating and doing other activities. Morning urine is highly concentrated and tends to be acidic. Because of the morning urine in the active ingredients is more sufficient, and not easy to destroy, not affected by diet, exercise and other factors, the most suitable for various tests. The second urine is the urine that is retained during the second urination after the morning urine. The second urine can reflect many states of urine, representing the real-time real situation of the urinary system, commonly used in routine urine testing. If you need to retain urine for laboratory tests, you should do so under the guidance of a professional physician and retain urine as prescribed by the doctor, rather than blindly retaining it on your own, which will affect the test results.