Various methods of measuring Glomerular Filtration Rate and Renal Plasma Flow

1. MEASURMENT OF GFR
AND RENAL PLASMA FLOW
FASLU RAHMAN CK
JOHNSON KL

2. GLOMERULAR FILTRATION RATE
Rate at which glomerular filtrate formed from plasma at glomerulus per minute per
unit area of body surface
GFR = Kf X net filtration pressure
Unit millilitters per minute
Normal 120 ml per minute
About 170 litter blood is filter through kidney
GFR is about 20% of renal plasma flow [RPF]

3. DETERMINATION OF GFR
RENAL CLEARANCE –kidney^s ability to remove substance from plasma
Features of substance used to measure GFR
1. Freely filtered from glomerulus
2. It should not be reabsorbed
3. It should not be secreated
4. Concentration in plasma = conc. In filtrate
5. It cant be degraded in body

4. DETERMINATION OF GFR
INULIN is the substance used commonly
Inulin – fructose polysaccharide
Its freely filtered,neither secreted nor reabsorbed.
Because inulin is not produced in our body ,rate of disappearance from blood after
i/v injection is strictly related to glomerular filtration.

5. GFR = Cinulin = Uinulin X V
Pinulin
Cinulin-vol. of plasma cleared of inulin per unit time
Uinulin-urine conc. Of inulin
V – volume of urine collected by time period of collection
P-plasma conc. Of inulin

6. Using endogenous creatinine clearance
 Creatinine is the endogenous by-product of muscle metabolism handled similar to
inulin
 Most widely used clinically – dose not reqire i/v
 In some species aprox. 10% is secreated.
 24 hour urine collection is reqired.
 Succesful in dog,cat,sheep&cattle

7. GFR = Ccre =Ucre
Pcre
In birds creatinine clearance cant used because avian renal tubule can secreat
creatinine when plasma level is elevated & can reabsorb when when plasma level is
normal
In clinical practice serum creatinine level – very small increase in serum creatinine
level – large reduction in GFR

8. RENAL PLASMA FLOW (RPF)
If a substance is completely cleared from plasma , clearance rate of that substance is
equal to total renal plasma flow.
Features of substance used to measure RPF
1. Freely filtered at the glomerulus
2. Not reabsorbed from tubular lumen
3. Must be secreated by tubular epithelium.

9. PAH (para amino hippuric acid) is commonly used to determine RPF
PAH is freely filtered by glomerular capilleris and is also secreated from peritubular
capillary blood into the tubular lumen
Total renal plasma flow = clearance of PAH /EPAH
Extraction ratio (EPAH) is calculated as difference between the renal arterial PAH
and renal venous PAH concenterations,divided by the renal arterial PAH
concenteration.

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