Kidney Function Assessment
The glomerular filtration rate (GFR) is equal to the sum of the filtration rates in all of the functioning nephrons; therefore, estimating the GFR gives a rough measure of the number of functioning nephrons.
Initial calculations utilized to estimate GFR in children relied heavily upon serum creatinine concentration.
Given the well-recognized influences on creatinine (ie, muscle mass) and the introduction of cystatin C as a reliable marker of renal function, a newer equation has since emerged. The “CKiD under 25” (also known as “U25”) is the most recently validated GFR estimating equation, which utilizes both age- and sex-specific constants “K” and incorporates creatinine as well as cystatin C.
The global nonprofit foundation Kidney Disease: Improving Global Outcomes (KDIGO) has stratified renal function in chronic kidney disease (CKD) based on the GFR.
See Table 1 below.
Table 1. CKD Stage (Open Table in a new window)
| CKD Stage* | GFR (mL/min/1.73 m2) |
|---|---|
| 1 | ≥90 |
| 2 | 60-89 |
| 3a | 45-59 |
| 3b | 30-44 |
| 4 | 15-29 |
| 5 | < 15 |
*The classification in Table 1 applies to children aged 2 years or older, because the GFR only becomes equivalent to that of adults between 1 and 2 years of age.