Base cohort and data sources
A base cohort was established by linking different Danish health
registries. The base cohort comprised all patients registered with at
least one INR measurement in the Copenhagen Primary Care Laboratory
(CopLab) database. The database includes laboratory test results from
primary health care patients in the Copenhagen area of Denmark from 2000
to 2015.16,17 During this period the primary health
care doctors in the Copenhagen area were served by the
Elective Laboratory of the Capital
Region (ELCR). ELCR covered approximately 1.2 million inhabitants and
provided a wide range of biochemical, physiological, and cardiac tests.
The CopLab database does not include INR point of care testing (POCT)
results from general practice. The ELCR was accredited for International
Organization for Standardization (ISO) standards ISO17025 and ISO15189.
Appendix A provides a detailed description of the INR assay.
For the cohort identified via CopLab, we retrieved data about drug use
from the Danish National Prescription Registry18 as
well as hospital diagnoses from the Danish National Patient Registry
(NPR).19 Data linkage was done using the unique Danish
Civil Registration Number assigned to all Danish
residents.20