GFR (Glomerular Filtration Rate)

About GFR (Glomerular Filtration Rate) ..

The radiopharmaceutical 99mTc-DTPA is ideal for measuring GFR because it is neither reabsorbed nor metabolised by the kidneys and only excreted from the kidney through glomerular filtration. Following IV injection of a known amount of radiopharmaceutical, three blood samples are collected at approximately 2-hourly intervals. The GFR is calculated by counting the radioactivity emitted from the blood samples (plasma clearance over time).  

GFR Samples WS.JPG 


  • Monitoring patients on renal toxic drugs eg. some types of chemotherapy

  • Kidney transplant donors

  • Clinical situations where an accurate GFR measurement is required. 


  • It is the responsibility of the department/ ward ordering the test to inform the patient.

  • NO IV fluids or diuretics from 6 hours before, or during the procedure.

  • NO Nuclear Medicine scans in the past 3 days or PET scans within 48 hours.

  • NO CT or MRI IV contrast either in the past 5 days or during the procedure.

  • NO recent radionuclide therapy.


  • The GFR test is usually performed on Wednesdays and Thursdays. Medical staff are advised to phone ext. 80867 to book the test, then send a requisition (include the test date and weight for patients >18yr).

  • Doses are prepared in the radiopharmacy and are ready to pick up at 08:45am. A GFR Instruction Sheet and Worksheet will accompany each dose.

  • Injection of the dose is the responsibility of the requesting department/ ward. It is important to allow time to gain venous access as the dose must be injected before 09:30.

  • If a dual lumen Hickman is used; withdraw heparin from the white lumen and flush with 5ml saline. Remove the PPD, inject the dose directly though the lumen and flush syringe with blood x 2 to ensure dose is completely through the lumen. Flush with 2 x 10ml saline using pulsatile flush and heplock under pressure as normal.

  • Keep the original needle and syringe along with any butterfly/ luer, swabs, saline flushes used during the injection and return to the Nuclear Medicine Department.

  • If any of the dose is spilt or tissued, the GFR calculation will not be accurate. If this is suspected, phone the department immediately to receive advice on whether or not to continue - the patient or items will need to be monitored by Nuclear Medicine staff.

  • Record the exact injection time on the Worksheet along with the patient's height and weight; these figures are used to correct the GFR result for body surface area.

  • Withdraw blood samples at approximately 2, 4 and 6 hours after the injection of the radioisotope. Use 10ml green top heparinised tubes and fill each tube to the same level. Full tube for adults, at least 5ml for children.

  • Collect the blood samples from another arm or at least a different vein from the injection site. If using a Hickman, take all samples from the red lumen and discard the first 5 ml of blood before sampling.

  • Note the exact time of each sampling on the worksheet. Sampling does not have to be exactly on the hour but the precise time of sampling must be noted – use the same clock/watch if possible.

  • Ensure the last sample is taken about 3pm and return all samples immediately to the Nuclear Medicine Department for processing by 3:15pm.

  • Results are usually available the same day.


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Page last reviewed: 23 March 2015