The Clinical Practice Research Datalink
The Clinical Practice Research Datalink (CPRD), known as the General Practice Research Database (GPRD) until March 2012, is a primary care database in the United Kingdom with links to other data resources such as cancer and death registries and hospital event statistics. The name of the database was changed to reflect the expanding types of data available to researchers.
The core of the CPRD is a database of anonymized patient records directly collected from hundreds of general practices throughout the United Kingdom. It is the world’s largest resource of anonymized longitudinal data from primary care, and currently contains data on over eight millions patients and over 50 million person-years of data. The characteristics of the United Kingdom health system, requiring general practitioners (GPs) to be the gatekeepers and coordinators of health care, make it an ideal setting to conduct epidemiologic research.
In the late 1980s the availability of computers in doctors’ offices began to change the medical record from a paper-based system to a computer-based system. At this time VAMP Health, working with the BCDSP, designed software for GPs to maintain their patient records on computers in the GP office. Those who chose to participate in the GPRD were provided with a computer and VAMP software. These GPs had a 12-month training period during which VAMP personnel work together with GPs and their staff to learn the routine, standardized procedures for the proper entering (and retrieval) of information on the computer. At the end of the 12-month training period, the computerized data were reviewed to determine whether the required information had been entered in a systematic, standardized manner. If the practice data were considered satisfactory, the information from that practice was made available for use in research. If the standards were not met the practice was informed and further instruction given to improve performance.
The computer record replaced the manual record for recording patient visits and includes information such as patient characteristics, drugs prescribed, clinical diagnoses, referrals to consultants, hospitalizations, and additional patient care information such as immunizations, laboratory results, certain historical information (e.g. medical history), and other patient data (e.g. smoking status, blood pressure, height, and weight). Referral letters from consultants and hospitalizations are kept in computer and manual files in the GPs office, and are available to researchers (after all identifying information is removed). All prescriptions are generated directly from the computer and are thus automatically part of the patient computer record. The details of each prescription, including dosage, instructions, and quantity are also automatically recorded on computer. The GPs also record the indication for each new course of drug therapy.
The CPRD is currently administered by the UK Medicines and Healthcare products Regulatory Agency (MHRA). The UK Department of Health (DoH) collects the information from GPs and routinely checks the data for accuracy and validity. In addition, before the data was initially used for research purposes, the BCDSP conducted extensive validation of the data [1,2]. The concordance between information on referrals and hospitalizations recorded on computer and information present in the practice paper medical record was greater than 90% in the first validation study  and greater than 95% in the second . Each subsequent study conducted by the BCDSP using GPRD data has confirmed these findings (see publications).
The BCDSP is licensed to receive regular data updates from the CPRD and to use the data for research purposes. Anonymized information from the CPRD on demographics, outpatient visits, hospitalizations and prescriptions dispensed is available to the researchers at the BCDSP. Validation of diagnoses, reports of diagnostic tests and anonymized notes from hospitalizations and referrals can be obtained from the general practitioner upon request. Additional data linkage (e.g. Hospital Episode Statistics (HES), cancer registries) is also available on a study-by-study basis. The BCDSP has worked with the GPRD (now CPRD) for 25 years and has published over 250 original research papers (see publications) using the GPRD (now the CPRD) resource.
 Jick H, Jick SS, Derby LE. Validation of information recorded on general practitioner based computerised data resource in the United Kingdom. BMJ 1991; 302: 766-8.
 Jick H, Terris BZ, Derby LE, Jick SS. Further validation of information recorded on a general practitioner based computerized data resource in the United Kingdom. Pharmacoepidemiol Drug Safety 1992; 1: 347-7.