Background
The Danish National Patient Registry (DNPR) is one of the world’s oldest nationwide hospital registries and is used extensively for research. Many studies have validated algorithms for identifying health events in the DNPR, but the reports are fragmented and no overview exists.

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The Danish National Patient Registry: a review of content, data quality, and research potential.

Objectives To evaluate the individual risk factors composing the CHADS 2 (Congestive heart failure, Hypertension, Age≥75 years, Diabetes, previous Stroke) score and the CHA 2 DS 2 -VASc (CHA 2 DS 2 -Vascular disease, Age 65-74 years, Sex category) score and to calculate the capability of the schemes to predict thromboembolism. Design Registry based cohort study. Setting Nationwide data on patients admitted to hospital with atrial fibrillation. Population All patients with atrial fibrillation not treated with vitamin K antagonists in Denmark in the period 1997-2006. Main outcome measures Stroke and thromboembolism. Results Of 121 280 patients with non-valvular atrial fibrillation, 73 538 (60.6%) fulfilled the study inclusion criteria. In patients at “low risk” (score=0), the rate of thromboembolism per 100 person years was 1.67 (95% confidence interval 1.47 to 1.89) with CHADS 2 and 0.78 (0.58 to 1.04) with CHA 2 DS 2 -VASc at one year’s follow-up. In patients at “intermediate risk” (score=1), this rate was 4.75 (4.45 to 5.07) with CHADS 2 and 2.01 (1.70 to 2.36) with CHA 2 DS 2 -VASc. The rate of thromboembolism depended on the individual risk factors composing the scores, and both schemes underestimated the risk associated with previous thromboembolic events. When patients were categorised into low, intermediate, and high risk groups, C statistics at 10 years’ follow-up were 0.812 (0.796 to 0.827) with CHADS 2 and 0.888 (0.875 to 0.900) with CHA 2 DS 2 -VASc. Conclusions The risk associated with a specific risk stratification score depended on the risk factors composing the score. CHA 2 DS 2 -VASc performed better than CHADS 2 in predicting patients at high risk, and those categorised as low risk by CHA 2 DS 2 -VASc were truly at low risk for thromboembolism.

https://www.bmj.com/content/bmj/342/bmj.d124.full.pdf

Validation of risk stratification schemes for predicting stroke and thromboembolism in patients with atrial fibrillation: nationwide cohort study

Background
The Charlson comorbidity index is often used to control for confounding in research based on medical databases. There are few studies of the accuracy of the codes obtained from these databases.

We examined the positive predictive value (PPV) of the ICD-10 diagnostic coding in the Danish National Registry of Patients (NRP) for the 19 Charlson conditions.

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The predictive value of ICD-10 diagnostic coding used to assess Charlson comorbidity index conditions in the population-based Danish National Registry of Patients

BACKGROUND AND PURPOSE: Epidemiological studies, mainly based on Western European surveys, have shown that stroke is more common in men than in women In recent years, sex-specific data on stroke i 

Sex Differences in Stroke Epidemiology A Systematic Review

METHODS Using Danish national registries, we identified all patients discharged from the hospital with a diagnosis of nonvalvular atrial fibrillation between 1997 and 2008 The risk of stroke or systemic thromboembolism and bleeding associated with non–end-stage chronic kidney disease and with end-stage chronic kidney disease (ie, disease requiring renal-replacement therapy) was estimated with the use of time-dependent Cox regression analyses In addition, the effects of treatment with warfarin, aspirin, or both in patients with chronic kidney disease were compared with the effects in patients with no renal disease RESULTS Of 132,372 patients included in the analysis, 3587 (27%) had non–end-stage chronic kidney disease and 901 (07%) required renal-replacement therapy at the time of inclusion As compared with patients who did not have renal disease, patients with non–end-stage chronic kidney disease had an increased risk of stroke or systemic thromboembolism (hazard ratio, 149; 95% confidence interval [CI], 138 to 159; P<0001), as did those requiring renal-replacement therapy (hazard ratio, 183; 95% CI, 157 to 214; P<0001); this risk was significantly decreased for both groups of patients with warfarin but not with aspirin The risk of bleeding was also increased among patients who had non–end-stage chronic kidney disease or required renalreplacement therapy and was further increased with warfarin, aspirin, or both CONCLUSIONS Chronic kidney disease was associated with an increased risk of stroke or systemic thromboembolism and bleeding among patients with atrial fibrillation Warfarin treatment was associated with a decreased risk of stroke or systemic thromboembolism among patients with chronic kidney disease, whereas warfarin and aspirin were associated with an increased risk of bleeding (Funded by the Lundbeck Foundation)

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Stroke and Bleeding in Atrial Fibrillation with Chronic Kidney Disease

Background: Many registers containing routine medical information have been developed for research and surveillance purposes. In epidemiological research assessment of endpoints is often conducted via registers. In the present study we validated stroke and transient ischemic attack (TIA) diagnoses in the Danish National Register of Patients (DNRP). Methods: Subjects from a Danish cohort study, the Copenhagen City Heart Study (n = 19,698), were crosslinked with the DNRP. The following International Classification of Disease 10th revision codes were used to identify possible strokes and TIAs: I60–I69 and G45. Two independent raters reviewed all cases. Positive predictive values of stroke, TIA and stroke subtypes were estimated by dividing the confirmed cases by the total number of cases located in the DNRP. Interrater reliability was tested using ĸ statistics. Results: Of 236 possible cerebrovascular events, 1 in 6 stroke diagnoses did not meet study criteria. The majority of events in the DNRP were registered as unspecified stroke (I64), n = 105 (44%), of which two thirds were diagnosed as ischemic stroke events by the raters. Intracerebral hemorrhage and ischemic stroke had a positive predictive value from 74 to 97%, respectively. Conclusion: Our results show that the DNRP tends to overestimate the number of cerebrovascular events, while ischemic stroke is underestimated.

Validity of Stroke Diagnoses in a National Register of Patients

Background and Purpose Stroke incidence has increased in some countries and decreased in others. After 20 years of intensive antihypertensive treatment the latter could be expected, and we have evaluated the sex-specific temporal trends in stroke incidence using 17 years of follow-up in the Copenhagen City Heart Study. Subjects and Methods Our cohort comprised 19 698 subjects living in Copenhagen, Denmark. They were invited for health examinations in the following time periods: 1976 through 1978, 1981 through 1983, and 1992 through 1994. Trends are presented for all persons who attended at least one of the two first examinations as well as the total cohort including nonresponders. Subjects between 45 and 84 years of age were followed from March 1, 1976 until March 1, 1993. Changes in age-specific stroke incidence were calculated by means of Poisson regression analysis. Results For subjects aged 45 to 64 years, no significant trends were observed, with an annual incidence rate ratio of 1.00 (95% confidence...

Trends in Stroke Incidence The Copenhagen City Heart Study

Background: Psychological stress and alcohol are both suggested as risk factors for stroke. Further, there appears to be a close relation between stress and alcohol consumption. Several experimental studies have found alcohol consumption to reduce the immediate effects of stress in a laboratory setting. We aimed to examine whether the association between alcohol and stroke depends on level of self-reported stress in a large prospective cohort. Methods: The 5,373 men and 6,723 women participating in the second examination of the Copenhagen City Heart Study in 1981–1983 were asked at baseline about their self-reported level of stress and their weekly alcohol consumption. The participants were followed-up until 31st of December 1997 during which 880 first ever stroke events occurred. Data were analysed by means of Cox regression modelling. Results: At a high stress level, weekly total consumption of 1–14 units of alcohol compared with no consumption seemed associated with a lower risk of stroke (adjusted RR: 0.57, 95% CI: 0.31–1.07). At lower stress levels, no clear associations were observed. Regarding subtypes, self-reported stress appeared only to modify the association between alcohol intake and ischaemic stroke events. Regarding specific types of alcoholic beverages, self-reported stress only modified the associations for intake of beer and wine. Conclusions: This study indicates that the apparent lower risk of stroke associated with moderate alcohol consumption is confined to a group of highly stressed persons. It is suggested that alcohol consumption may play a role in reducing the risk of stroke by modifying the physiological or psychological stress response.

Is the effect of alcohol on risk of stroke confined to highly stressed persons

Stroke incidence and case-fatality in two populations

Three hundred and seventy-four general practitioners (GPs) in Denmark filled in a questionnaire on attitudes to include information on gender and diet in the strategy for prevention of coronary heart disease, cancer, osteoporosis, and overweight/underweight. Risk factors for disease in general were ranked as follows: smoking, alcohol, stress, diet, physical exercise, heredity and hygiene. The patients' lack of motivation, insufficient time for each patient, and inadequate knowledge about nutrition were stated as barriers to dietary counselling. The GPs stated that the gender of the patient was important only to the counselling on osteoporosis. Lack of time and insufficient knowledge were perceived as barriers for including gender specific issues in prevention. It is concluded that GPs consider dietary counselling important but lack time and knowledge. The results point at a need for better pre- and postgraduate training in nutrition, and for a better reimbursement system for time spent on prevention.

G. Boysen

Papers

Validity of Stroke Diagnoses in a National Register of Patients

Trends in Stroke Incidence The Copenhagen City Heart Study

Is the effect of alcohol on risk of stroke confined to highly stressed persons

Stroke incidence and case-fatality in two populations

Attitude of general practitioners to the importance of gender and diet in disease prevention