This document discusses Denmark's national health registries and their use for epidemiological research. It notes that Denmark assigns unique personal identification numbers to all citizens, allowing accurate linkage between various health registries. This enables large population-based cohort studies with long-term follow up. The registries contain information on healthcare utilization, prescriptions, and diagnoses. Several studies are described that use the registries to study topics like MMR vaccination and autism, quality of diabetes care, and blood pressure control. Challenges with using registry data include ensuring validity of diagnoses and missing data. However, strengths include no selection bias, large sample sizes, and prospectively collected data.

1. ”When an entire country is a cohort”
Frank, Science 2000
”The epidemiologist’s dream:
Denmark”
Frank, Science 2003

2. Several important papers

3. Denmark - The epidemiologist’s
dream?

4. Data landscape

5. Personal Registration Number
All Danish citizens are assigned a unique civil registration
number (CPR), which enables accurate linkage between
these registries.
Danish Civil Registration system, including:
• Current and historical information on address in Denmark
(municipality, street, house number)
• Information on address is complete from 1971

6. Data
Danish Civil Registration system, including:
• Current and historical information on address in Denmark
(municipality, street, house number)
• Information on address is complete from 1971

7. Strengths of Danish data sources
• Public health care system
• Record linkage at the individual level
• Time and money saving
• Data-collection independent of research question
• Large populations and long-term follow up
• Liberal data law enabling data access
• Relatively inexpensive to get data

8. Validity
Positive predictive value (%)

9. Storage of administrative
patient data
Storage of medical
patient data
Use of a computer
during consultation
Use of a decision support
system via a health portal
(www.sundhed.dk)
E-mail consultation and renewal
of medication
Transfer of medical
patient data to
other carers
Denmark has the worlds’ most “computerised” general practice
Transfer of lab results
from the laboratory
Patients receive results
from laboratory by mail

10. Sentinel Data capture
PC in
clinic
PC in
clinic
Server
in
clinic
DAMD
Server
NIP
National
Indicator
Project
DAMD
Report
server
Danish healthcare
data net
Transferring data
from DAMD til NIP
DAMD generates quality feedback reports
GPs have access to reports from their
patient group through secure logon
Quality feedback reports are generated individually for each practice on
the basis of the accumulated data and available online only for the
specific practice.
The feedback reports includes a benchmark section which enables the
GP to compare his own quality with other GPs locally
and nationally.
pop-up

13. Proportion of diabetes patients, percent
HbA1c, median
Total cholesterol , median
Systolic blood-pressure, median
Percent of patients investigated last year
Percent of patients investigated last year
Percent of patients investigated last year
Percent of patients investigated last year
U-Alb/Crea, median

14. Wakefield Lancet
1998
Timing of symptoms
MMR and Autism

15. Vaccination cohort
Registries
Civil Registration system, Central psychiatric Register,
National Hospital Register, Medical Birth Register, National
Health Service
Cohort
Danish children born 1991-1998 (N= 537,000)
MMR vaccinated (N=439,251)
Outcome
Autism (N= 316), Autism spectrum disorder (N= 422)
Febrile seizures (N=17,986)

16. MMR
vaccination
Autism
Autism spectrum
disorder
No
Yes
1.00 (reference)
0.92 (0.68-1.24)
1.00 (reference)
0.83 (0.65-1.07)
MMR and Autism

17. Does feedback improve diabetes care?
• DAMD – Danish General Practice Database (Oct. 2009)
~ 506,000 patients
~ 14,500 patients with type 2 diabetes
We included patients with type 2 diabetes with at least two
diabetes recordings (yearly controls) from Oct. 2009 to Oct. 2010
• The number of included patients was 7988;
5805 with recorded bloodpressure
7122 with recorded cholesterol levels

18. Oct. 2009,
N(%)
Oct. 2010,
N(%)
Absolute risk
reduction (95% CI)
Diabetes control (HbA1c>7% and
no antidiabetic medication)
235 (2.94) 127 (1.59)
1.35%(0.89-1.81),
p<0.001
Bloodpressure (Systolic>130 and
no antihypertensive medication)
722 (12.44) 460 (7.92)
4.51%(3.42-5.61),
p<0.001
Cholesterol (>4.5 mmol/l and no
cholesterol-lowering medication)
1226
(17.21)
889 (12.48)
4.73% (3.56-5.90),
p<0.001
Proportion of patients with values above recommendations among the
7988 included type 2 diabetes patients
(5805 with recorded bloodpressure, 7123 with recorded cholesterol levels)

20. Results
• BP control rate 33.2% (CI: 32.7-33.7).
• BP control rate, diabetes: 16.5% (CI: 15.8-17.3)
• BP control rate, comorbidities: 42.9% - 51.4% for
patients with ischemic heart diseases,
cerebrovascular or peripheral vascular diseases.
• Other comorbidities such as cancer, psychiatric
disease or chronic obstructive pulmonary diseases,
never reduced the odds of BP control

21. Challenges
• Validity of the diagnoses
• Missings data

30. Strengths
• No selection bias
• Size matters
• Data is collected prosepctively

31. Data Protection in Denmark
• Complies with European Union rules
• Waives the need for informed consent when data are
used for ”statistical and scientific purposes of significance
to society”
• Stipulates rules for handeling of data
• Allows the use of individual information while minimizing
• the spread of these data
• No breaches after more than thirty years

32. Informed consent is a cornerstone in
all medical research
The Helsinki Declaration: ‘the health of my patient will be
my first consideration’ and ‘while the goal of the primary
purpose of medical research is to generate new knowledge,
this goal can never take precedence over the rights and
interests of individual research subjects’.

33. ”If we are using data that already exist and the research can
be done with no risk for the people under study, there may
well more ethical problems in not doing the research than in
doing it. ”

34. Most countries record births, deaths and several diseases,
and some in addition record use of medicine, treatment
procedure, diagnostic data etc. Much of this is done
without having informed consent.
Getting informed consent after data collection will be
difficult, in most cases even impossible.
The existence of these data is a threat to privacy, but not
necessarily in the use of the data for research.

35. No date – no knowledge – no
development
Quality assurance
Research
CME

36. Aerobec Initial analyses

37. Inclusion
Initiation cohort EF Total
All 1086 84294
At least 1 outcome
ICS
860 61649
1 yr bsl and 1 yr
outcome
854 61237
Exclude ICS/LABA
FDC*
726 57780
Exclude COPD** 666 54773
No maintenance
OS
661 54570
*R03AK07 or 08, **LAMA during baseline or outcome period

38. Step-up cohort EF Non-EF
All 164 61125
At least 1 outcome
ICS
147 51664
1 yr bsl and 1 yr
outcome
147 51425
Excluding ICS/LABA
FDC*
137 48364
Excluding COPD** 130 45672
No maintenance
OS
130 45331
*At least 1 baseline ICS and 50% step-up at
index date

39. Severe exercabations
Initiation
Cohort
Non-EF EF Total
No Severe
Exer.
48197 (89%) 602 (91%) 48799 (89%)
At least 1
Sev. Exer.
5712 (11%) 59 (9%) 5771 (11%)
Total 53909
(100%)
661 (100%) 54570
(100%)