**4.4 Conclusion**

8 Basic Nephrology and Acute Kidney Injury

heavy person. We may conclude that indexation of the GFR is necessary to allow

**DATA SMALL PERSON HEAVY PERSON** 

In this case, we study the evolution of a healthy boy during his childhood. In Table 3 the age, length, weight, BSA, absolute GFR and cGFR of the boy at the age of 3.5, 7.5, 11 and 15 years are listed. For the average healthy boy, the corrected cGFR remains constant during childhood (from 2-3 years till 14 years) (Piepsz et al., 2008, 2009) but the absolute GFR values of the boy at different ages cannot be compared with each other. From the data in Table 3 or by inspection of Figure 2, one may observe an increasing absolute GFR, as well as an increasing BSA as a function of age because the child and his kidneys are still growing. Referring to our pond analogy, one could say that the pump and filter combination of the pond are constantly changing in order to keep the pond clearance at the same rate. Correcting GFR for BSA leads to the same clearance value, independent of age. With the corrected cGFR, the child's kidney function can be followed, regardless of his growth

Fig. 2. (A) Absolute GFR as a function of age; (B) BSA as a function of age; (C) cGFR as a

It is known that the GFR shows an age-dependent decline for the average healthy person, which may be considered as part of the normal biological process of senescence. The body weight is also often increasing with age. That is why in this case we study the GFR of two adult men, one with a stable weight during adulthood and one with a weight that increases with age (Table 4). The man with a stable weight has a normal age-dependent decreasing

**Age (years)** 55 55 **Length (cm)** 150 190 **Weight (kg)** 50 100 **BSA (m²)** 1.43 2.28 **GFR (ml/min)** 60 60 **cGFR (ml/min/1.73m²)** 73 46

Table 2. Data for comparison of the GFR of a small and heavy person.

A. B. C.

comparison between different patients.

**4.2 Case 2: GFR evolution during childhood**

**4.3 Case 3: GFR evolution during adulthood** 

process.

function of age.

The cases described above illustrate that indexation is necessary to compare patient values with each other and with reference values. But the question remains whether BSA is the appropriate index for GFR. This has been a subject of debate during the last ten years.
