Validity of estimated prevalence of decreased kidney function and renal replacement therapy from primary care electronic health records compared with national survey and registry data in the United Kingdom

Background. Anonymous primary care records are an important resource for observational studies. However, their external validity is unknown in identifying the prevalence of decreased kidney function and renal replacement therapy (RRT). We thus compared the prevalence of decreased kidney function and RRT in the Clinical Practice Research Datalink (CPRD) with a nationally representative survey and national registry. Methods. Among all people >= 25 years of age registered in the CPRD for >= 1 year on 31 March 2014, we identified patients with an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m(2), according to their most recent serum creatinine in the past 5 years using the Chronic Kidney Disease Epidemiology Collaboration equation and patients with recorded diagnoses of RRT. Denominators were the entire population in each age-sex band irrespective of creatinine measurement. The prevalence of eGFR < 60 mL/min/1.73 m(2) was compared with that in the Health Survey for England (HSE) 2009/2010 and the prevalence of RRT was compared with that in the UK Renal Registry (UKRR) 2014. Results. We analysed 2 761 755 people in CPRD [mean age 53 (SD 17) years, men 49%], of whom 189 581 (6.86%) had an eGFR < 60 mL/min/1.73 m(2) and 3293 (0.12%) were on RRT. The prevalence of eGFR < 60 mL/min/1.73 m2 in CPRD was similar to that in the HSE and the prevalence of RRT was close to that in the UKRR across all age groups in men and women, although the small number of younger patients with an eGFR < 60 mL/min/1.73 m(2) in the HSE might have hampered precise comparison. Conclusions. UK primary care data have good external validity for the prevalence of decreased kidney function and RRT.