4. Measurement of Renal Function

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Summary of Terms and Equations for Renal Physiology

 

UNITS 

SYMBOLS

EQUATIONS
Concentration      
  of solute, s  mg/ml, g/l, mg/dl, mM, mEq/l

[s]p or Ps

  
  mass/vol. 

Eq/ml, mOsm/kg H2O

[s]u or Us

  
Rate of Excretion      
  Water, vol./time 

ml/min, ml/24 hrs

V

  
  Solute, mass/time mg/min, Eq/min, osmole/min  

= UsV
Clearance of a solute      

Vol. of plasma cleared of a solute

      
  Vol./time

ml/min

Cs

= UsV/Ps
Filtration rate      
  Water, vol./time 

ml/min,

 GFR, Cin, Ccr = UinV/Pin or UcrV/Pcr
  Solute, mass/time 

mg/min, Eq/min, moles/min

  

= PsGFR, or PsCin or PsCcr
Rate of Tubular Transport      

Reabsorption or Secretion

      
  Water, vol./time

ml/min,

  

=GFR-V,

  Solute, mass/time

mg/min,Eq/min, moles/min

Ts

=PsGFR-UsV (reab) or UsV- PsGFR (sec)
Concentration Ratio      
  Urine:Plasma

none

U/P, Us/Ps

  
Fractional Rate of Excretion      

Fraction of the filtered amt. that is excreted

      
  Water % FEH2O = Pcr/Ucr (x100)
  Solute   % FEs = (U/P)s/(U/P)cr (x100)
Fractional Rate of Reabsorption      

Fraction of the filtered amt. that is reabsorbed.

      
  Water  % FRH2O = 100-FEH2O
  Solute  % FRs = 100-FEs

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