Commonly performed in patients considering kidney donation for transplant
More accurate than estimated GFR
GFR: Plasma volume presented to nephrons per unit time (mL/min)
Normal GFR: Young adults ~ 120 mL/min/1.73 m², decreases normally with age
Nuclear Medicine GFR Analysis
Radionuclide administered IV to patient
Counts obtained on plasma samples over time counted in gamma counter and compared to standard sample
Utilizes radionuclides that are cleared by glomerular filtration
Use same clock for entire procedure day
Ideal characteristics of GFR analysis radiopharmaceutical
Only glomerular filtration, where plasma = urinary clearance
Low molecular weight and small molecular size allows free glomerular membrane filtration
Inert otherwise: No protein binding, no cellular metabolism, no traveling across cells, not renal toxic, no excretion besides by kidneys, no tubular excretion/absorption
Inulin is gold standard for GFR measurement; not used because expensive, time-consuming, technically difficult: Multiple urine samples required; difficult in people with urologic disease, children
Needs to not dissociate from radioactive moiety
Usually lab-based procedure but can also be performed through gamma camera imaging
Lab Procedure
Confirm patient has not had another nuclear medicine study or therapy recently (confirm 4 half-lives since study/therapy)
Reliable for patients > 3 months old; however, may be spurious in patients up until ~ 2 years due to continual maturation of renal parenchyma from 0-2 years
Tracer preparation
Patient dose and standard dose drawn from radiopharmacy supply (2 doses total needed)
Record
Quantity of patient dose and standard dose (volume, activity or weight)
Time of measurement
Patient weight
Radiopharmaceuticals
Tc-99m diethylenetriaminepentaacetic acid (DTPA): Confirm purity (> 98%), may dissociate
Adult dose: 2-10 mCi (74-370 MBq); higher end used if imaging in addition to GFR analysis
Pediatric dose: 1 mCi (37 MBq) max
t1/2: 6 hours (count samples within 24 hours of blood draw)
t1/2: 27.7 days (can count samples at later time due to long t1/2; waste storage requires long time)
Reliable for GFR > 30 mL/min
Administration
Administer patient dose IV
Confirm no extravasation using gamma camera
If extravasation, study is not valid and needs to be repeated
Flush with normal saline
Record
Time of administration
Residual volume, activity or weight of administration syringe
Sample
Obtain venous blood sample on limb opposite that of administration (10 mL in adults, 7 mL in children)
2 samples at 2-hour interval: 1 and 3 hours or 2 and 4 hours
Record time samples obtained
Isolate plasma through centrifugation of sample
Prepare ~ 1 mL plasma (two 1-mL samples can be prepared for each time point; helps to detect errors)
Standard sample drawn from standard solution then diluted
Prepare ~ 1 mL standard (two 1-mL samples can be prepared; helps to detect errors)
Background sample
Prepare ~ 1 mL water
Counting
Standard, background, plasma
Count each sample for > 10K counts
May dilute samples to avoid dead-time errors; dilute all samples similarly
Apply decay correction for plasma and standard samples
Usually use well counter, but counts can also be obtained with gamma camera
Each sample should be counted twice
GFR calculation
To reduce errors, check input count values, calculations, times, as well as agreement between 2 samples of same type at same time
2-sample method (slope-intercept)
Clearance is expressed as injected dose divided by area under plasma curve
Normalize to 1.73 m² using formula: BSA (cm) = [wt (kg)] ⁰·⁴²⁵ x [ht (cm)] ⁰·⁷²⁵ x 71.84
Selected References
Bibbo G et al: Comparison of glomerular filtration rates determined using two- and single-blood sample methods with a three-blood sample technique for 2922 paediatric studies. Nucl Med Commun. 40(12):1204-10, 2019
McMeekin H et al: 99mTc DTPA vs. 51Cr EDTA for glomerular filtration rate measurement: is there a systematic difference? Nucl Med Commun. 40(12):1224-9, 2019
Lam NN et al: Renal and cardiac assessment of living kidney donor candidates. Nat Rev Nephrol. 13(7):420-8, 2017
Murray AW et al: Assessment of glomerular filtration rate measurement with plasma sampling: a technical review. J Nucl Med Technol. 41(2):67-75, 2013
Related Anatomy
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Related Differential Diagnoses
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References
Tables
Tables
KEY FACTS
Terminology
Radiopharmaceuticals
TERMINOLOGY
Definitions
Glomerular filtration rate (GFR) analysis
Commonly performed in patients considering kidney donation for transplant
More accurate than estimated GFR
GFR: Plasma volume presented to nephrons per unit time (mL/min)
Normal GFR: Young adults ~ 120 mL/min/1.73 m², decreases normally with age
Nuclear Medicine GFR Analysis
Radionuclide administered IV to patient
Counts obtained on plasma samples over time counted in gamma counter and compared to standard sample
Utilizes radionuclides that are cleared by glomerular filtration
Use same clock for entire procedure day
Ideal characteristics of GFR analysis radiopharmaceutical
Only glomerular filtration, where plasma = urinary clearance
Low molecular weight and small molecular size allows free glomerular membrane filtration
Inert otherwise: No protein binding, no cellular metabolism, no traveling across cells, not renal toxic, no excretion besides by kidneys, no tubular excretion/absorption
Inulin is gold standard for GFR measurement; not used because expensive, time-consuming, technically difficult: Multiple urine samples required; difficult in people with urologic disease, children
Needs to not dissociate from radioactive moiety
Usually lab-based procedure but can also be performed through gamma camera imaging
Lab Procedure
Confirm patient has not had another nuclear medicine study or therapy recently (confirm 4 half-lives since study/therapy)
Reliable for patients > 3 months old; however, may be spurious in patients up until ~ 2 years due to continual maturation of renal parenchyma from 0-2 years
Tracer preparation
Patient dose and standard dose drawn from radiopharmacy supply (2 doses total needed)
Record
Quantity of patient dose and standard dose (volume, activity or weight)
Time of measurement
Patient weight
Radiopharmaceuticals
Tc-99m diethylenetriaminepentaacetic acid (DTPA): Confirm purity (> 98%), may dissociate
Adult dose: 2-10 mCi (74-370 MBq); higher end used if imaging in addition to GFR analysis
Pediatric dose: 1 mCi (37 MBq) max
t1/2: 6 hours (count samples within 24 hours of blood draw)
t1/2: 27.7 days (can count samples at later time due to long t1/2; waste storage requires long time)
Reliable for GFR > 30 mL/min
Administration
Administer patient dose IV
Confirm no extravasation using gamma camera
If extravasation, study is not valid and needs to be repeated
Flush with normal saline
Record
Time of administration
Residual volume, activity or weight of administration syringe
Sample
Obtain venous blood sample on limb opposite that of administration (10 mL in adults, 7 mL in children)
2 samples at 2-hour interval: 1 and 3 hours or 2 and 4 hours
Record time samples obtained
Isolate plasma through centrifugation of sample
Prepare ~ 1 mL plasma (two 1-mL samples can be prepared for each time point; helps to detect errors)
Standard sample drawn from standard solution then diluted
Prepare ~ 1 mL standard (two 1-mL samples can be prepared; helps to detect errors)
Background sample
Prepare ~ 1 mL water
Counting
Standard, background, plasma
Count each sample for > 10K counts
May dilute samples to avoid dead-time errors; dilute all samples similarly
Apply decay correction for plasma and standard samples
Usually use well counter, but counts can also be obtained with gamma camera
Each sample should be counted twice
GFR calculation
To reduce errors, check input count values, calculations, times, as well as agreement between 2 samples of same type at same time
2-sample method (slope-intercept)
Clearance is expressed as injected dose divided by area under plasma curve
Normalize to 1.73 m² using formula: BSA (cm) = [wt (kg)] ⁰·⁴²⁵ x [ht (cm)] ⁰·⁷²⁵ x 71.84
Selected References
Bibbo G et al: Comparison of glomerular filtration rates determined using two- and single-blood sample methods with a three-blood sample technique for 2922 paediatric studies. Nucl Med Commun. 40(12):1204-10, 2019
McMeekin H et al: 99mTc DTPA vs. 51Cr EDTA for glomerular filtration rate measurement: is there a systematic difference? Nucl Med Commun. 40(12):1224-9, 2019
Lam NN et al: Renal and cardiac assessment of living kidney donor candidates. Nat Rev Nephrol. 13(7):420-8, 2017
Murray AW et al: Assessment of glomerular filtration rate measurement with plasma sampling: a technical review. J Nucl Med Technol. 41(2):67-75, 2013
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