Kidney Disease Cohort (KidDiCo) of Southern Denmark: Design, Coverage, Generalizability and Implications for Use.

Background This article provides a description of a large register of a population from the Region of Southern Denmark, the Kidney Disease Cohort (KiDiCo). Coverage and representativeness according to gender and education level are discussed. Methods Data for KiDiCo were obtained using laboratory databases from participating laboratories in the Region of Southern Denmark and were linked to individual personal 10-digit personal identification numbers. The study population includes individuals over 18 years of age living in Denmark, whose serum creatinine was analysed in one of the 27 participating laboratories in the Region of Southern Denmark during the period of 8 years from 1st January 2006 to 31st December 2013. Individually linked data consist of diagnosis codes, date and cause of death, dispensed medicine data, socioeconomic data and demographic data. Results In total, n = 669,929 individuals had their blood tested for creatinine between 2007 and 2013 in a defined geographical area. The estimated geographical coverage was 78%. The median age of the background population was 6 years lower. The cohort had a slightly higher percentage of females (53%) compared to the background population (49%). Differences in educational levels reflect the minor age gap. Conclusion Based on coverage of 78% together with similar characteristics in terms of gender and age, the KiDiCo is a representative cohort of patients in the Region of Southern Denmark. Combining laboratory data with high-quality Danish administrative registers makes diverse research feasible.