Abstract
Purpose
Measurements of glomerular filtration rate (GFR) are frequently interpreted assuming a linear variation with age. Nonlinear relationships may give a better representation of the changes associated with normal ageing.
Methods
This was a retrospective study of 904 subjects (468 women, 436 men; age range 18–84 years) undergoing assessment as prospective living kidney donors. GFR was evaluated from 51Cr-EDTA plasma clearance using blood samples taken at 2, 3 and 4 h. The slope–intercept GFR was corrected for body surface area (BSA) using the Haycock formula and for the fast exponential using the Brochner-Mortensen equation. The relationship between age, gender and GFR was examined using best-fit curve analysis. Nonlinear relationships with age were explored using fractional polynomials.
Results
There was no gender difference in BSA-corrected GFR over five decades of age (P = 0.40). However, female donors with a body mass index >30 kg/m2 had a statistically significantly lower GFR than nonobese women (P < 0.01). The best-fit relationship between age and GFR was nonlinear and described using a fractional polynomial model of degree 1 (GFR = 103.9–0.0061 × Age2 mL/min/1.73 m2) with a root mean standard error of 12.9 mL/min/1.73 m2. The residual variance for this model was significantly smaller than for the best-fit linear model (P = 0.006).
Conclusions
GFR measurements in prospective living kidney donors are best corrected for age using a nonlinear relationship.
Measurements of glomerular filtration rate (GFR) are frequently interpreted assuming a linear variation with age. Nonlinear relationships may give a better representation of the changes associated with normal ageing.
Methods
This was a retrospective study of 904 subjects (468 women, 436 men; age range 18–84 years) undergoing assessment as prospective living kidney donors. GFR was evaluated from 51Cr-EDTA plasma clearance using blood samples taken at 2, 3 and 4 h. The slope–intercept GFR was corrected for body surface area (BSA) using the Haycock formula and for the fast exponential using the Brochner-Mortensen equation. The relationship between age, gender and GFR was examined using best-fit curve analysis. Nonlinear relationships with age were explored using fractional polynomials.
Results
There was no gender difference in BSA-corrected GFR over five decades of age (P = 0.40). However, female donors with a body mass index >30 kg/m2 had a statistically significantly lower GFR than nonobese women (P < 0.01). The best-fit relationship between age and GFR was nonlinear and described using a fractional polynomial model of degree 1 (GFR = 103.9–0.0061 × Age2 mL/min/1.73 m2) with a root mean standard error of 12.9 mL/min/1.73 m2. The residual variance for this model was significantly smaller than for the best-fit linear model (P = 0.006).
Conclusions
GFR measurements in prospective living kidney donors are best corrected for age using a nonlinear relationship.
| Original language | English |
|---|---|
| Pages (from-to) | 1445-1452 |
| Number of pages | 8 |
| Journal | International Urology and Nephrology |
| Volume | 45 |
| Issue number | 5 |
| DOIs | |
| Publication status | Published - Oct 2013 |