Age Changes in Renal Function 



231 



Although there is a substantial variation between subjects at 

 any given age, the trend is highly significant.* 



The age decrement in glomerular filtration rate, as measured 

 by standard inulin clearance, is shown in Fig. 2. The regres- 

 sion of inulin clearance with age is expressed by the equation : 

 C1t„ = 153*2 — 0-96 X age (in years). The average decline 



^In 



over the age span 20-90 years was 46 per cent in this instance.| 



20 



30 



40 



60 



70 



80 



90 



50 



AGE-YEARS 

 Fig. 2. Change in standard inulin clearance or glomerular filtration 



rate with age. O O average values, ml. filtrate/min./l • 73 sq. m. 



body surface area. 



(From; Shock, 1952). 



The fall in glomerular filtration rate is closely associated with 

 the fall in plasma flow so that the filtration fraction, calculated 

 as ratio of inulin clearance to the diodrast clearance, shows 

 only a slight increase with age (Fig. 3). 



* In a different sample of subjects in whom renal plasma flow was estimated 

 from PAH (/?-aminohippuric acid) clearance (Watkin and Shock, 1955), the 

 regression equation was: CIpah = 820 — 6-75 X age (in years). 



f In other groups of subjects the regression of inulin clearance on age was : 

 Clin = 157-0 — 1-16 X age (in years) (Watkin and Shock, 1955), and 

 Clin = 150-9 — 0-904, X age (Miller, McDonald and Shock, 1952). 



