Low glomerular filtration rate but polyuria may be caused by chronic nephritis, hypertensive nephropathy, etc. Glomerular filtration rate can directly reflect the degree of glomerular damage and renal function impairment. Glomerular filtration rate can directly reflect the degree of glomerular damage and impaired renal function, usually <90ml/min suggests that the glomerular filtration rate is lowered. 24-hour urine volume of more than 2,500ml is known as polyuria, low glomerular filtration rate and urinary polyuria may be due to the following reasons. 1. Chronic nephritis: chronic nephritis patients with reduced renal function, glomerular filtration rate is reduced, at the same time, the tubular concentration of urine function is reduced, which can cause polyuria, which is manifested in the day and night urinary output is abnormal, the phenomenon of nocturia increased. 2. Hypertensive nephropathy: Hypertensive nephropathy patients with elevated creatinine, glomerular filtration rate is reduced, but also may appear increased nocturia, proteinuria, swelling of the lower limbs and other symptoms. If the glomerular filtration rate is low but the urine is high, you should go to the hospital in time to find out the reason and standardize the treatment under the doctor's guidance.