A kidney stone (renal calculus) lodges in a ureter, blocking the flow of urine..

Glomerular filtration rate: The total amount of plasma filtrate formed by all the nephrons of the kidneys per minute; it is determined physiologically by three factors:  (1) the total surface area available for filtration, (2) the permeability of the filtration membrane, and (3) the net filtration pressure; normally, (1) and (2) do not change in healthy individuals, though they can be changed by injuries and disease processes; therefore, the body normally adjusts GFR by adjusting net filtration pressure (see above calculations) in the kidneys; therefore, GFR is proportional to net filtration pressure; it is measured by a variety of clinical tests known as renal clearance studies, of which the creatinine clearance test is the most popular; a typical GFR in healthy individuals is 120-125 mL/min.

Renal calculi (kidney stones) will tend to decrease NFP as they increase in size or number because they will obstruct the outward flow of urine from the kidney and create a back pressure in the renal tubules and collecting ducts.  That back pressure will increase Capsular Hydrostatic Pressure (CHP).

NFP and GFR are directly proportional.  As NFP increases, GFR increases; as NFP decreases, GFR decreases.

Depending on the size of the stone and where it is lodged, the effect can range from absolutely nothing (in other words, the GFR stays perfectly normal) to complete shut down of kidney function (the GFR drops to less than 10%, to the point where the person goes into kidney failure).

Most of us are born with two healthy kidneys, and either one can sustain the body's need on its own. So if a small kidney stone blocks off a small section of kidney, GFR as a whole will not change.

On the other hand, a stone lodged in the bladder neck (and thus blocking off urine from BOTH kidneys) is enough to cause enough back pressure for both kidneys to shut down. Often, the shut down is reversible, so dialysis is not needed if a urologist or interventional radiologist can restore urine flow (by removing the stone or putting in a nephrostomy drain).