Glomerular Filtration Rate (GFR) Study

Preparation Requirements
Total duration of study:

4 hours

Bleeding time:

2 blood samples are taken 1-2 and 3-4 hours post injection


Not contraindicated but clear clinical indication is required

Breast feeding:

Stopped for duration of study. Mothers are advised to express milk prior to study.


Recent U&E is required

Previous studies:



Some drugs can reduce renal function e.g. diuretics (frusemide), aminoglycoside antibiotics, penicillins, sulphonamides and aluminium (Blathen et al, 1978) and therefore all medications being taken should be recorded prior to the study being performed.


Patient is encouraged to drink water prior and during study


Excessive intake of drinks containing caffeine including tea, coffee and Coke should be avoided after 10 pm the night before the test because of their diuretic effect (Clomius et al, 1979). Protein load may increase GFR (Wilkinson et al, 1991) and it is recommended to avoid high protein meals before the study. Since neither carbohydrate nor fat loads affect GFR, a light meal, low in protein would optimise accuracy and reproducibility. (Levine et al, 1986). A light breakfast is recommended. If the test straddles the lunch period then a light lunch e.g. sandwiches can be taken.

Exercise has been shown to have a variable effect on GFR (Merrill et al, 1948, Kachadorian et al, 1970, Wilkinson et al, 1991). Strict bed rest is unnecessary, but some restriction of activity is necessary for good reproducibility.