Final answer:
Creatinine is the non-protein nitrogenous compound used to measure the glomerular filtration rate (GFR), which is an indicator of kidney function.
Step-by-step explanation:
The glomerular filtration rate (GFR) is a critical indicator of kidney function, representing the volume of fluid filtered from the renal glomerular capillaries into Bowman's capsule per unit time. While inulin clearance is a precise measure of GFR, it is cumbersome in clinical settings. Hence, creatinine, a waste product of muscle metabolism, is often used due to its convenient characteristics: it is freely filtered by the glomerulus and minimally secreted by renal tubules, providing a reliable approximation of GFR. Urea, uric acid, and ammonia are other non-protein nitrogenous substances involved in renal function assessment but do not measure GFR as effectively as creatinine.
The creatinine clearance test involves calculating the GFR by comparing urine creatinine concentrations with those in the plasma, accounting for urine flow rate. Estimating GFR with creatinine is essential for determining appropriate drug dosages and understanding the excretory performance of the kidneys. Other tests, like the urea clearance test, do not provide a direct measure of GFR but can also offer insights into renal function.
"What non-protein nitrogenous compound measures the GFR?" is a) Creatinine.