Golisano Children's Hospital / Pediatric Nephrology / Measurement of Glomerular Filtration Rate (GFR) Measurement of Glomerular Filtration Rate (GFR) This test measures how well the kidneys filter waste products from the body. A tiny amount of non-radioactive material (less than that used in a chest x-ray) is injected into the blood stream. Blood is drawn two hours and five hours later to assess how well the kidneys have filtered out the material. This test is available only as a research study, if indicated.