Background: Following the introduction of routine calculation of estimated glomerular filtration rate (eGFR) from all serum creatinine values in samples received from general practice it was noted that there was a preponderance of values consistent with chronic kidney disease (CKD) stage 3 or higher.

Methods: A review was conducted of all eGFR values from 51 314 individuals received from primary care during October 2006 to April 2007.

Results: It was found that more than 25% of eGFR results indicated CKD stage 3 or higher. The median age in this group was 64 years (range 18–104 years) while that of the local general population according to the 2001 census was 40 years (range 18–104 years); these ages were statistically significantly different (p<0.001). There was no difference between the groups with regard to gender. The eGFR data were therefore corrected for age distribution, and an estimated prevalence of 5.6% of eGFR consistent with CKD stage 3 was found. This was a higher proportion than estimates of CKD suggested before the introduction of eGFR.

Conclusions: The higher proportion of CKD stage 3 may be due to difference in age and gender in populations studied, as there is a marked effect of age on calculated eGFR values found.