Increase in GFR can be due to:

Glomerular filtration is the first step in the formation of urine and is carried out by the glomerulus. GFR or glomerular filtration rate is the amount of the filtrate formed by the kidneys per minute. The factors playing a role in filtration are blood colloidal osmotic pressure, capsular hydrostatic pressure, capillary blood pressure and glomerular hydrostatic pressure. The increase in colloidal osmotic pressure will lead to decrease in GFR as the increased colloid will prevent effective filtration. Increase in capsular hydrostatic pressure will push the filtrate back into the capillaries and thus reduce the GFR. Decrease in glomerular hydrostatic pressure means the pressure of the blood in the capillaries which will lead to decrease in GFR where as an increase in capillary blood pressure will increase the rate of filtration.