The so-called renal threshold is the highest concentration of a substance that is absorbed by the renal tubules. Many substances in the body, including water, electrolytes, and sugars, are filtered through the glomerulus and then reabsorbed through the renal tubules. But the absorption of substances by the renal tubules is not unlimited, there is also a certain absorption capacity, beyond which the renal tubules will no longer absorb and can be detected in the urine. Take blood sugar as an example, if blood sugar is below 8.8mmol/L, the sugar filtered from the glomerulus will basically be reabsorbed through the renal tubules, so the detection of urine sugar in the urine is negative. If the patient’s blood sugar is poorly controlled and exceeds 8.8 mmol/L, some of the sugar filtered through the glomerulus exceeds the reabsorption capacity of the renal tubules and will appear in the urine. The urine sugar will be found to be positive when the urine routine is tested, and this condition can be called as the blood sugar exceeds the renal sugar threshold.