The Danish health care system and epidemiological research: from health care contacts to database records

Denmark has a large network of population-based medical databases, which routinely collect high-quality data as a by-product of health care provision. The Danish medical databases include administrative, health, and clinical quality databases. Understanding the full research potential of these data sources requires insight into the underlying health care system. This review describes key elements of the Danish health care system from planning and delivery to record generation. First, it presents the history of the health care system, its overall organization and financing. Second, it details delivery of primary, hospital, psychiatric, and elderly care. Third, the path from a health care contact to a database record is followed. Finally, an overview of the available data sources is presented. This review discusses the data quality of each type of medical database and describes the relative technical ease and cost-effectiveness of exact individual-level linkage among them. It is shown, from an epidemiological point of view, how Denmark’s population represents an open dynamic cohort with complete long-term follow-up, censored only at emigration or death. It is concluded that Denmark’s constellation of universal health care, long-standing routine registration of most health and life events, and the possibility of exact individual-level data linkage provides unlimited possibilities for epidemiological research.

Positive predictive value of cardiovascular diagnoses in the Danish National Patient Registry: a validation study

OBJECTIVE

The majority of cardiovascular diagnoses in the Danish National Patient Registry (DNPR) remain to be validated despite extensive use in epidemiological research. We therefore examined the positive predictive value (PPV) of cardiovascular diagnoses in the DNPR.

DESIGN

Population-based validation study.

SETTING

1 university hospital and 2 regional hospitals in the Central Denmark Region, 2010-2012.

PARTICIPANTS

For each cardiovascular diagnosis, up to 100 patients from participating hospitals were randomly sampled during the study period using the DNPR.

MAIN OUTCOME MEASURE

Using medical record review as the reference standard, we examined the PPV for cardiovascular diagnoses in the DNPR, coded according to the International Classification of Diseases, 10th Revision.

RESULTS

A total of 2153 medical records (97% of the total sample) were available for review. The PPVs ranged from 64% to 100%, with a mean PPV of 88%. The PPVs were ≥90% for first-time myocardial infarction, stent thrombosis, stable angina pectoris, hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, takotsubo cardiomyopathy, arterial hypertension, atrial fibrillation or flutter, cardiac arrest, mitral valve regurgitation or stenosis, aortic valve regurgitation or stenosis, pericarditis, hypercholesterolaemia, aortic dissection, aortic aneurysm/dilation and arterial claudication. The PPVs were between 80% and 90% for recurrent myocardial infarction, first-time unstable angina pectoris, pulmonary hypertension, bradycardia, ventricular tachycardia/fibrillation, endocarditis, cardiac tumours, first-time venous thromboembolism and between 70% and 80% for first-time and recurrent admission due to heart failure, first-time dilated cardiomyopathy, restrictive cardiomyopathy and recurrent venous thromboembolism. The PPV for first-time myocarditis was 64%. The PPVs were consistent within age, sex, calendar year and hospital categories.

CONCLUSIONS

The validity of cardiovascular diagnoses in the DNPR is overall high and sufficient for use in research since 2010.

Migraine and risk of cardiovascular diseases: Danish population based matched cohort study

OBJECTIVE

To examine the risks of myocardial infarction, stroke (ischaemic and haemorrhagic), peripheral artery disease, venous thromboembolism, atrial fibrillation or atrial flutter, and heart failure in patients with migraine and in a general population comparison cohort.

DESIGN

Nationwide, population based cohort study.

SETTING

All Danish hospitals and hospital outpatient clinics from 1995 to 2013.

PARTICIPANTS

51 032 patients with migraine and 510 320 people from the general population matched on age, sex, and calendar year.

MAIN OUTCOME MEASURES

Comorbidity adjusted hazard ratios of cardiovascular outcomes based on Cox regression analysis.

RESULTS

Higher absolute risks were observed among patients with incident migraine than in the general population across most outcomes and follow-up periods. After 19 years of follow-up, the cumulative incidences per 1000 people for the migraine cohort compared with the general population were 25 v 17 for myocardial infarction, 45 v 25 for ischaemic stroke, 11 v 6 for haemorrhagic stroke, 13 v 11 for peripheral artery disease, 27 v 18 for venous thromboembolism, 47 v 34 for atrial fibrillation or atrial flutter, and 19 v 18 for heart failure. Correspondingly, migraine was positively associated with myocardial infarction (adjusted hazard ratio 1.49, 95% confidence interval 1.36 to 1.64), ischaemic stroke (2.26, 2.11 to 2.41), and haemorrhagic stroke (1.94, 1.68 to 2.23), as well as venous thromboembolism (1.59, 1.45 to 1.74) and atrial fibrillation or atrial flutter (1.25, 1.16 to 1.36). No meaningful association was found with peripheral artery disease (adjusted hazard ratio 1.12, 0.96 to 1.30) or heart failure (1.04, 0.93 to 1.16). The associations, particularly for stroke outcomes, were stronger during the short term (0-1 years) after diagnosis than the long term (up to 19 years), in patients with aura than in those without aura, and in women than in men. In a subcohort of patients, the associations persisted after additional multivariable adjustment for body mass index and smoking.

CONCLUSIONS

Migraine was associated with increased risks of myocardial infarction, ischaemic stroke, haemorrhagic stroke, venous thromboembolism, and atrial fibrillation or atrial flutter. Migraine may be an important risk factor for most cardiovascular diseases.

Existing Data Sources in Clinical Epidemiology: Laboratory Information System Databases in Denmark

Routine biomarker results from hospital laboratory information systems, covering hospitals and general practitioners, in Denmark are available to researchers through access to the regional Clinical Laboratory Information System Research Database at Aarhus University and the nationwide Register of Laboratory Results for Research. This review describes these two data sources. The laboratory databases have different geographical and temporal coverage. They both include individual-level biomarker results that are electronically transferred from laboratory information systems. The biomarker results can be linked to all other Danish registries at the individual level, using the unique identifier, the CPR number. The databases include variables such as the CPR number, date and time (hour and minute) of sampling, NPU code, and name of the biomarker, identification code for the laboratory and the requisitioner, the test result with the corresponding unit, and the lower and upper reference limits. Access to the two databases differs since they are hosted by two different institutions. Data cannot be transferred outside Denmark, and direct access is provided only to Danish institutions. It is concluded that access to data on routine biomarkers expands the detailed biological and clinical information available on patients in the Danish healthcare system. The full potential is enabled through linkage to other Danish healthcare registries.

Positive predictive value of cardiac examination, procedure and surgery codes in the Danish National Patient Registry: a population-based validation study

OBJECTIVE

Danish medical registries are widely used for cardiovascular research, but little is known about the data quality of cardiac interventions. We computed positive predictive values (PPVs) of codes for cardiac examinations, procedures and surgeries registered in the Danish National Patient Registry during 2010-2012.

DESIGN

Population-based validation study.

SETTING

We randomly sampled patients from 1 university hospital and 2 regional hospitals in the Central Denmark Region.

PARTICIPANTS

1239 patients undergoing different cardiac interventions.

MAIN OUTCOME MEASURE

PPVs with medical record review as reference standard.

RESULTS

A total of 1233 medical records (99% of the total sample) were available for review. PPVs ranged from 83% to 100%. For examinations, the PPV was overall 98%, reflecting PPVs of 97% for echocardiography, 97% for right heart catheterisation and 100% for coronary angiogram. For procedures, the PPV was 98% overall, with PPVs of 98% for thrombolysis, 92% for cardioversion, 100% for radiofrequency ablation, 98% for percutaneous coronary intervention, and 100% for both cardiac pacemakers and implantable cardiac defibrillators. For cardiac surgery, the overall PPVs was 99%, encompassing PPVs of 100% for mitral valve surgery, 99% for aortic valve surgery, 98% for coronary artery bypass graft surgery, and 100% for heart transplantation. The accuracy of coding was consistent within age, sex, and calendar year categories, and the agreement between independent reviewers was high (99%).

CONCLUSIONS

Cardiac examinations, procedures and surgeries have high PPVs in the Danish National Patient Registry.

Heart failure and risk of dementia: a Danish nationwide population-based cohort study

AIMS

The association between heart failure and dementia remains unclear. We assessed the risk of dementia among patients with heart failure and members of a general population comparison cohort.

METHODS AND RESULTS

Individual-level data from Danish medical registries were linked in this nationwide population-based cohort study comparing patients with a first-time hospitalization for heart failure between 1980 and 2012 and a year of birth-, sex-, and calendar year-matched comparison cohort from the general population. Stratified Cox regression analysis was used to compute 1-35-year hazard ratios (HRs) for the risk of all-cause dementia and, secondarily, Alzheimer's disease, vascular dementia, and other dementias. Analyses included 324 418 heart failure patients and 1 622 079 individuals from the general population (median age 77 years, 52% male). Compared with the general population cohort, risk of all-cause dementia was increased among heart failure patients [adjusted HR 1.21, 95% confidence interval (CI) 1.18-1.24]. The associations were stronger in men and in heart failure patients under age 70. Heart failure patients had higher risks of vascular dementia (adjusted HR 1.49, 95% CI 1.40-1.59) and other dementias (adjusted HR 1.30, 95% CI 1.26-1.34) than members of the general population cohort. Heart failure was not associated with Alzheimer's disease (adjusted HR 1.00, 95% CI 0.96-1.04).

CONCLUSION

Heart failure was associated with an increased risk of all-cause dementia. Heart failure may represent a risk factor for dementia, but not necessarily for Alzheimer's disease.

Risk of Dementia in Adults With Congenital Heart Disease: Population-Based Cohort Study

BACKGROUND

More children with congenital heart disease (CHD) are surviving to adulthood, and CHD is associated with risk factors for dementia. We compared the risk of dementia in CHD adults to that of the general population.

METHODS

In this cohort study, we used medical registries and a medical record review covering all Danish hospitals to identify adults with CHD diagnosed between 1963 and 2012. These individuals with CHD were followed from January 1, 1981, 30 years of age, or date of first CHD registration (index date for matched members of the general population cohort) until hospital diagnosis of dementia, death, emigration, or end of study (December 31, 2012). For each individual with CHD, we identified 10 members of the general population utilizing the Danish Civil Registration System matched on sex and birth year. We computed cumulative incidences and hazard ratios (HRs) of dementia, adjusting for sex and birth year.

RESULTS

The cumulative incidence of dementia was 4% by 80 years of age in 10 632 adults with CHD (46% male). The overall HR comparing adults with CHD with the general population cohort was 1.6 (95% confidence interval [CI], 1.3-2.0). The HR among individuals with CHD without extracardiac defects was 1.4 (95% CI, 1.1-1.8). Adults with mild-to-moderate CHD had an HR of 1.5 (95% CI, 1.1-2.0), whereas the HR was 2.0 (95% CI, 1.2-3.3) for severe CHD, including univentricular hearts. The HR for early onset dementia (<65 years of age) was 2.6 (95% CI, 1.8-3.8), whereas the late-onset HR was 1.3 (95% CI, 1.0-1.8).

CONCLUSIONS

CHD was associated with an increased risk of dementia compared with the general population, in particular for early onset dementia. Further understanding of dementia risk in the population with CHD is a potential target for future investigation.

Risk of Stroke in Patients With Heart Failure

Background and Purpose—

The long-term risk of specific stroke subtypes among heart failure patients is largely unknown. We examined short-term and long-term risk of ischemic stroke, intracerebral hemorrhage (ICH), and subarachnoid hemorrhage (SAH) in heart failure patients and in a general population comparison cohort.

Methods—

In this nationwide cohort study (1980−2012), we used Danish population-based medical registries to identify and follow (1) all patients hospitalized for the first time with heart failure and (2) a birth year–, sex-, and calendar year–matched general population comparison cohort. Age-, sex-, and comorbidity-adjusted stroke rate ratios were computed based on Cox regression analysis.

Results—

We included 289 353 patients with heart failure and 1 446 765 individuals from the general population in the analysis. One- and 5-year risks among heart failure patients were 1.4% and 3.9% for ischemic stroke, 0.2% and 0.5% for ICH, and 0.03% and 0.07% for SAH. The 30-day adjusted stroke rate ratio was increased markedly for ischemic stroke (5.08; 95% confidence interval, 4.58–5.63] and was also elevated for ICH (2.13; 95% confidence interval, 1.53–2.97) and SAH (3.52; 95% confidence interval, 1.54–8.08). Between 31 days and 30 years, risk of all stroke subtypes remained positively associated with heart failure (1.5- to 2.1-fold for ischemic stroke, 1.4- to 1.8-fold for ICH, and 1.1- to 1.7-fold for SAH) in comparison with the general population cohort.

Conclusions—

Heart failure was associated with increased short-term and long-term risk of all stroke subtypes, suggesting that heart failure is a potent and persistent risk factor for ischemic stroke, ICH, and SAH.

Thirty-Year Mortality After Coronary Artery Bypass Graft Surgery: A Danish Nationwide Population-Based Cohort Study

BACKGROUND

Data are sparse on long-term mortality after coronary artery bypass graft (CABG) surgery. We examined short-term and long-term mortality of patients undergoing CABG surgery and a general population comparison cohort.

METHODS AND RESULTS

Linking data from Danish registries, we conducted a nationwide, population-based cohort study on 51 307 CABG patients and 513 070 individuals from the general population matched on age, sex, and calendar year (1980-2009). The mortality risk was higher in patients having isolated CABG surgery than in the general population, particularly during 0 to 30 days (3.2% versus 0.2%), 11 to 20 years (51.1% versus 35.6%), and 21 to 30 years (62.4% versus 44.8%), but not substantially higher during 31 to 364 days (2.9% versus 2.4%) or 1 to 10 years (30.7% versus 25.8%). The 30-day adjusted mortality rate ratio for isolated CABG surgery was 13.51 (95% confidence interval [CI], 12.59-14.49). Between 31 to 364 days and 1 to 10 years, the isolated CABG surgery cohort had a slightly higher mortality rate than the general population comparison cohort, adjusted mortality rate ratios of 1.15 (95% CI, 1.09-1.21) and 1.09 (95% CI, 1.08-1.11), respectively. Between 11 to 20 years and 21 to 30 years, the adjusted mortality rate ratios were 1.62 (95% CI, 1.58-1.66) and 1.76 (95% CI, 1.62-1.91). Within 30 days, CABG patients had a 25-fold, a 26-fold, and a 18-fold higher risk of dying from myocardial infarction, heart failure, or stroke, respectively, than members of the general population comparison cohort. We found substantial heterogeneity in absolute mortality rates according to baseline risk groups.

CONCLUSIONS

The isolated CABG cohort had a higher mortality rate than the general population comparison cohort, especially within 30 days of and 10 years after surgery.

Disseminated intravascular coagulation: epidemiology, biomarkers, and management

Disseminated intravascular coagulation (DIC) is a systemic activation of the coagulation system, which results in microvascular thrombosis and, simultaneously, potentially life-threatening haemorrhage attributed to consumption of platelets and coagulation factors. Underlying conditions, e.g. infection, cancer, or obstetrical complications are responsible for the initiation and propagation of the DIC process. This review provides insights into the epidemiology of DIC and the current understanding of its pathophysiology. It details the use of diagnostic biomarkers, current diagnostic recommendations from international medical societies, and it provides an overview of emerging diagnostic and prognostic biomarkers. Last, it provides guidance on management. It is concluded that timely and accurate diagnosis of DIC and its underlying condition is essential for the prognosis. Treatment should primarily focus on the underlying cause of DIC and supportive treatment should be individualised according to the underlying aetiology, patient's symptoms and laboratory records.

Thromboembolic and bleeding complications during oral anticoagulation therapy in cancer patients with atrial fibrillation: a Danish nationwide population-based cohort study

Coexisting cancer in patients with atrial fibrillation (AF) has been associated with thromboembolism and bleeding. We used Danish population‐based medical databases to conduct a population‐based cohort study that included all AF patients who redeemed a prescription for vitamin K antagonists (VKA) or non‐VKA oral anticoagulant (NOAC) between July 2004 and December 2013. We characterized these patients according to the presence (N = 11,855) or absence (N = 56,264) of a cancer diagnosis before redemption of their oral anticoagulant prescription, and then examined their 1‐year risk of thromboembolic or bleeding complications or death. We next used Cox regression to compare the hazard ratios for complications among VKA‐ or NOAC‐treated AF patients with versus without a cancer diagnosis, after adjusting for sex, age, and CHA₂DS₂VASc score. One‐year risks of thromboembolic complications in AF patients who redeemed a VKA prescription were similar in those with (6.5%) and without (5.8%) cancer [hazard ratio (HR) 1.0 (95% confidence interval (CI): 0.93, 1.1)]. This also was found for bleeding complications (5.4% vs. 4.3%, HR 1.1 [95% CI: 1.0, 1.2]). For AF patients with cancer who redeemed a NOAC prescription, risks were also similar for thromboembolic complications (4.9% of cancer patients vs. 5.1% of noncancer patients, HR 0.80 [95% CI: 0.61, 1.1]), and for bleeding complications (4.4% vs. 3.1%, HR 1.2 [95% CI: 0.92, 1.7]). The absolute risks of thromboembolic or bleeding complications were nearly the same in patients with and without cancer who redeemed prescription for VKAs or NOACs.

Sampling strategies for selecting general population comparison cohorts

Background

For a patient cohort, access to linkable population-based registries permits sampling of a comparison cohort from the general population, thereby contributing to the understanding of the disease in a population context. However, sampling without replacement in random order can lead to immortal time bias by conditioning on the future.

Aim

We compared the following strategies for sampling comparison cohorts in matched cohort studies with respect to time to ischemic stroke and mortality: sampling without replacement in random order; sampling with replacement; and sampling without replacement in chronological order.

Methods

We constructed index cohorts of individuals from the Danish general population with no particular trait, except being alive and without ischemic stroke on the index date. We also constructed index cohorts of persons aged >50 years from the general population. We then applied the sampling strategies to sample comparison cohorts (5:1 or 1:1) from the Danish general population and compared outcome risks between the index and comparison cohorts. Finally, we sampled comparison cohorts for a heart failure cohort using each strategy.

Results

We observed increased outcome risks in comparison cohorts sampled 5:1 without replacement in random order compared to the index cohorts. However, these increases were minuscule unless index persons were aged >50 years. In this setting, sampling without replacement in chronological order failed to sample a sufficient number of comparators, and the mortality risks in these comparison cohorts were lower than in the index cohorts. Sampling 1:1 showed no systematic difference between comparison and index cohorts. When we sampled comparison cohorts for the heart failure patients, we observed a pattern similar to when index persons were aged >50 years.

Conclusion

When index persons were aged >50 years, ie, had high outcome risks, sampling 5:1 without replacement introduced bias. Sampling with replacement or 1:1 did not introduce bias.

Elevated potassium levels in patients with chronic kidney disease: occurrence, risk factors and clinical outcomes-a Danish population-based cohort study

Background

Data on the true burden of hyperkalemia (HK) in patients with chronic kidney disease (CKD) in a real-world setting are scarce.

Methods

The incidence rate of HK [first blood test with an elevated blood potassium level level >5.0 mmol/L] in primary or hospital care was assessed in a population-based cohort of all newly diagnosed CKD patients [second estimated glomerular filtration rate (eGFR) measurement <60 mL/min/1.73 m2 or hospital diagnosis] in northern Denmark. Risk factors and clinical outcomes were compared for CKD patients with HK and matched CKD patients without HK.

Results

Of 157 766 patients with CKD, 28% experienced HK, for an overall HK incidence rate of 70/1000 person-years. Among patients with Stage 3A, 3B, 4 or 5 CKD, 9, 18, 31 and 42%, respectively, experienced HK within the first year. Important HK risk factors included diabetes {prevalence ratio [PR] 1.74 [95% confidence interval (CI) 1.69-1.79]}, heart failure [PR 2.31 (95% CI 2.23-2.40)] and use of angiotensin-converting enzyme inhibitors [PR 1.45 (95% CI 1.42-1.48)], potassium supplements [PR 1.59 (95% CI 1.55-1.62)] or spironolactone [PR 2.53 (95% CI 2.44-2.63)]. In CKD patients who developed HK, 34% had any acute hospitalization 6 months before the HK event, increasing to 57% 6 months after HK [before-after risk ratio 1.72 (95% CI 1.69-1.74)]. The 6-month mortality following HK was 26%, versus 6% in matched non-HK patients. Compared with non-HK patients, 6-month hazard ratios for any acute hospitalization in HK patients were 2.11-fold higher, including hazard ratios of 2.07 for cardiac diagnoses, 2.29 for ventricular arrhythmias, 3.26 for cardiac arrest, 4.77 for intensive care and 4.85 for death.

Conclusions

More than one in four CKD patients develops HK. Patients with severe CKD, diabetes, heart failure or use of spironolactone are at high risk. HK is associated with severe clinical outcomes.

Elevated Potassium Levels in Patients With Congestive Heart Failure: Occurrence, Risk Factors, and Clinical Outcomes: A Danish Population-Based Cohort Study

Background

Data on the true burden of hyperkalemia in patients with heart failure (HF) in a real‐world setting are limited.

Methods and Results

Incidence rates of hyperkalemia (first blood test with a potassium level >5.0 mmol/L) in primary or hospital care were assessed in a population‐based cohort of patients with incident HF diagnoses in northern Denmark from 2000 to 2012. Risk factors and clinical outcomes were compared in patients with HF with versus without hyperkalemia. Of 31 649 patients with HF, 39% experienced hyperkalemia (mean follow‐up, 2.2 years). Risks of experiencing a second, third, or fourth event were 43%, 54%, and 60%, respectively. Among patients with HF with stage 3A, 3B, 4, or 5 kidney dysfunction, 26%, 35%, 44%, and 48% experienced hyperkalemia within the first year. Important hyperkalemia risk factors included chronic kidney disease (prevalence ratio, 1.46; 95% confidence interval [CI], 1.43−1.49), diabetes mellitus (prevalence ratio, 1.38; 95% CI, 1.32−1.45), and spironolactone use (prevalence ratio, 1.48; 95% CI, 1.42−1.54). In patients with HF who developed hyperkalemia, 53% had any acute‐care hospitalization 6 months before the hyperkalemia event, increasing to 74% 6 months after hyperkalemia (before‐after risk ratio, 1.41; 95% CI, 1.38−1.44). Compared with matched patients with HF without hyperkalemia, adjusted 6‐month hazard ratios in patients with hyperkalemia were 2.75‐fold (95% CI, 2.65–2.85) higher for acute‐care hospitalization and 3.39‐fold (95% CI, 3.19–3.61) higher for death.

Conclusions

Almost 4 in 10 patients with HF develop hyperkalemia, and many patients have recurrent hyperkalemia episodes. Hyperkalemia risk is strongly associated with degree of reduced kidney function and use of spironolactone. Hyperkalemia is associated with severe clinical outcomes and death in HF.

Risks of Stroke Recurrence and Mortality After First and Recurrent Strokes in Denmark: A Nationwide Registry Study

BACKGROUND AND OBJECTIVES

To examine risks of stroke recurrence and mortality after first and recurrent stroke.

METHODS

Using Danish nationwide health registries, we included patients age ≥18 years with first-time ischemic stroke (n = 105,397) or intracerebral hemorrhage (ICH) (n = 13,350) from 2004 to 2018. Accounting for the competing risk of death, absolute risks of stroke recurrence were computed separately for each stroke subtype and within strata of age groups, sex, stroke severity, body mass index, smoking, alcohol use, Essen stroke risk score, and atrial fibrillation. Mortality risks were computed after first and recurrent stroke.

RESULTS

After adjusting for competing risks, the overall 1-year and 10-year risks of recurrence were 4% and 13% following first-time ischemic stroke and 3% and 12% following first-time ICH. For ischemic stroke, the risk of recurrence increased with age and was higher for men and following mild vs more severe stroke. The most marked differences were across Essen risk scores, for which recurrence risks increased with increasing scores. For ICH, risks were similar for both sexes and did not increase with Essen risk score. For ischemic stroke, the 1-year and 10-year risks of all-cause mortality were 17% and 56% after a first-time stroke and 25% and 70% after a recurrent stroke; corresponding estimates for ICH were 37% and 70% after a first-time event and 31% and 75% after a recurrent event.

DISCUSSION

The risk of stroke recurrence was substantial following both subtypes, but risks differed markedly among patient subgroups. The risk of mortality was higher after a recurrent than first-time stroke.

Cardiovascular and bleeding outcomes in a population-based cohort of patients with chronic immune thrombocytopenia

Essentials Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by low platelet count. We conducted a cohort study of 3 584 chronic ITP patients from the Nordic countries. Cardiovascular events occurred across all platelet count levels. Cardiovascular or bleeding events were strong prognostic factors for all-cause mortality. Background Among patients with chronic immune thrombocytopenia (cITP), little is known regarding risk factors for cardiovascular and bleeding outcomes and how these events influence mortality. Objectives We examined the rate of cardiovascular events and bleeding requiring a hospital contact according to platelet count levels, as well as the prognostic impact of these events on all-cause mortality in adult patients with cITP. Methods We identified all cITP patients registered in the Nordic Country Patient Registry for Romiplostim during 1996 to 2015. Absolute risks and hazard ratios across platelet count levels based on Cox regression analysis were computed, adjusting for age, sex, prevalent/incident cITP, smoking, and comorbidities. We also compared all-cause mortality rates in cITP patients with and without cardiovascular and bleeding events. Results Among 3 584 cITP patients, 1-year risks were 1.9% for arterial cardiovascular events, 1.2% for venous thromboembolism, and 7.5% for bleeding. Rates of cardiovascular events were similar across platelet counts. Patients with platelet counts <50 × 109 /L had >2-fold higher rates of bleeding than patients with normal platelet counts. These associations were unchanged in time-varying analyses that considered changes in platelet counts during follow-up. Occurrences of cardiovascular and bleeding events were associated with 4-fold to 5-fold increases in 1-year mortality. Conclusions Among patients with cITP, the 1-year risks of cardiovascular events were 1% to 2%, while nearly 8% experienced a bleeding event within 1 year. Cardiovascular events occurred across all platelet levels, while low platelet counts were associated with increased hazards of bleeding. Cardiovascular and bleeding events were strong prognostic factors for mortality.

Pregnancy, Birth, Neonatal, and Postnatal Neurological Outcomes After Pregnancy With Migraine

BACKGROUND

Prevalence of migraine is high during the reproductive age. Although migraine often improves during pregnancy, the risk of adverse pregnancy, birth, neonatal, and neurological outcomes in mother and offspring remains poorly understood.

OBJECTIVE

To investigate the associations between maternal migraine and risks of adverse pregnancy outcomes in the mother, and birth, neonatal and postnatal outcomes in the offspring.

METHODS

We used Danish population registries to assemble a cohort of pregnancies among women with migraine and an age- and conception year-matched comparison cohort of pregnancies among women without migraine. The study period was 2005-2012. We computed adjusted prevalence ratios (aPRs) for pregnancy and birth outcomes and adjusted risk ratios (aRRs) for neonatal and postnatal outcomes, adjusting for age, preconception medical history, and preconception reproductive history.

RESULTS

We identified 22,841 pregnancies among women with migraine and 228,324 matched pregnancies among women without migraine. Migraine was associated with an increased risk of pregnancy-associated hypertension disorders (aPR: 1.50 [95% confidence interval (CI): 1.39-1.61]) and miscarriage (aPR: 1.10 [95% CI: 1.05-1.15]). Migraine was associated with an increased prevalence of low birth weight (aPR: 1.14 [95% CI: 1.06-1.23]), preterm birth (aPR: 1.21 [95% CI: 1.13-1.30]) and cesarean delivery (aPR: 1.20 [95% CI: 1.15-1.25]), but not of small for gestational age offspring (aPR: 0.94 [95% CI: 0.88-0.99]) and birth defects (aPR: 1.01 [95% CI: 0.93-1.09]). Offspring prenatally exposed to maternal migraine had elevated risks of several outcomes in the neonatal and postnatal period, including intensive care unit admission (aRR: 1.22 [95% CI: 1.03-1.45]), hospitalization (aRR: 1.12 [95% CI: 1.06-1.18]), dispensed prescriptions (aRR: 1.34 [95% CI: 1.24-1.45]), respiratory distress syndrome (aRR: 1.20 [95% CI: 1.02-1.42]), and febrile seizures (aRR: 1.27 [95% CI: 1.03-1.57), but not of death (aRR: 0.67 [95% CI: 0.43-1.04]) and cerebral palsy (aRR: 1.00 [95% CI: 0.51-1.94]).

CONCLUSIONS

Women with migraine and their offspring have greater risks of several adverse pregnancy outcomes than women without migraine.

Change in body mass index from childhood onwards and risk of adult cardiovascular disease

Childhood obesity adversely affects the structure and function of the cardiovascular system, but the relationship between excessive weight gain during childhood and adult cardiovascular disease (CVD) is not fully understood. This review summarizes evidence for associations of change in body mass index (BMI) from childhood onwards with CVD outcomes. We found that excessive gain in BMI from childhood onwards was consistently associated with the presence of CVD risk factors, with increased risks of coronary heart disease, and there were suggestions of associations with stroke, atrial fibrillation and heart failure, but a lack of evidence precludes firm conclusions. These results indicate that the risk of CVD can be traced back to child ages and highlights the importance of primordial prevention of CVD by preventing excessive weight gain in childhood.

Risk of thromboembolic and bleeding outcomes following hematological cancers: A Danish population-based cohort study

BACKGROUND

Therapeutic advances have improved survival after hematological cancers. In turn, patients may be at increased risk of thromboembolic and bleeding events.

OBJECTIVES

To examine the risks of myocardial infarction (MI), ischemic stroke, venous thromboembolism (VTE), and bleeding requiring hospital contact in patients with hematological cancers.

METHODS

We conducted a Danish population-based cohort study (2000-2013). We identified all adult hematological cancer patients and sampled a general population comparison cohort in a 1:5 ratio matched by age, sex, previous thromboembolic events, bleeding, and solid cancer. Ten-year absolute risks of thromboembolism and bleeding were calculated and hazard ratios (HRs) were computed, controlling for matching factors.

RESULTS

Among 32 141 hematological cancer patients, the 10-year absolute risk of any thromboembolic or bleeding complication following hematological cancer was 19%: 3.3% for MI, 3.5% for ischemic stroke, 5.2% for VTE, and 8.5% for bleeding. Except among patients with myeloid leukemia, acute lymphoid leukemia, or myelodysplastic syndrome, the risk of thromboembolic events surpassed that of bleeding. The hematological cancer cohort overall was at increased risk for MI [HR = 1.36, 95% confidence interval (CI): 1.25-1.49], ischemic stroke (HR = 1.22, 95% CI: 1.12-1.33), VTE (HR = 3.37, 95% CI: 3.13-3.64), and bleeding (HR = 2.39, 95% CI: 2.26-2.53) compared with the general population.

CONCLUSIONS

Approximately 2 of 10 hematological cancer patients experienced MI, ischemic stroke, VTE, or bleeding requiring hospital contact within 10 years. The hematological cancer cohort had higher hazards of MI, ischemic stroke, VTE, and bleeding requiring hospital contact than a general population comparison cohort.

Risk and Prognosis of Cancer After Lower Limb Arterial Thrombosis

BACKGROUND

Venous thromboembolism can be a presenting symptom of cancer, but the association between lower limb arterial thrombosis and cancer is unknown. We therefore examined cancer risk and prognosis of cancer in patients with lower limb arterial thrombosis.

METHODS

Using nationwide population-based Danish medical registries, we identified all patients diagnosed with first-time lower limb arterial thrombosis (1994-2013) and followed them until the occurrence of any subsequent cancer diagnosis, emigration, death, or November 30, 2013, whichever came first. We computed standardized incidence ratios with 95% confidence intervals as the observed number of cancers relative to the expected number based on national incidence rates by sex, age, and calendar year. To examine the prognostic impact of lower limb arterial thrombosis on all-cause mortality after cancer, we constructed a matched comparison cohort of patients who had cancer without lower limb arterial thrombosis.

RESULTS

Among 6600 patients with lower limb arterial thrombosis, we observed 772 subsequent cancers. The risk of any cancer was 2.5% after 6 months of follow-up, increasing to 17.9% after 20 years. During the first 6 months of follow-up, the standardized incidence ratio of any cancer was 3.28 (95% confidence interval, 2.79-3.82). The standardized incidence ratio remained elevated during 7 to 12 months (1.42; 95% confidence interval, 1.09-1.83) and beyond 12 months (1.14; 95% confidence interval, 1.05-1.24). The strongest associations were found for lung cancer and other smoking-related cancers. Lower limb arterial thrombosis also was associated with increased all-cause mortality after colon, lung, urinary bladder, and breast cancer, but not after prostate cancer.

CONCLUSIONS

Lower limb arterial thrombosis was a marker of occult cancer, especially lung cancer, and was an adverse prognostic factor for mortality in common cancers.

Nationwide Trends in Incidence and Mortality of Stroke Among Younger and Older Adults in Denmark

OBJECTIVE

To investigate the extent to which the incidence and mortality of a first-time stroke among younger and older adults changed from 2005 to 2018 in Denmark using nationwide registries.

METHODS

We used the Danish Stroke Registry and the Danish National Patient Registry to identify patients 18 to 49 years of age (younger adults) and those ≥50 years of age (older adults) with a first-time ischemic stroke, intracerebral hemorrhage, or subarachnoid hemorrhage. We computed age-standardized incidence rates and 30-day and 1-year mortality risks separately for younger and older adults and according to smaller age groups, stroke subtype, sex, and severity (Scandinavian Stroke Scale score). Average annual percentage changes (AAPCs) were computed to assess temporal trends.

RESULTS

We identified 8,680 younger adults and 105,240 older adults with an ischemic stroke or intracerebral hemorrhage. The incidence rate per 100,000 person-years of ischemic stroke (20.8 in 2005 and 21.9 in 2018, AAPC -0.6 [95% confidence interval (CI) -1.5 to 0.3]) and intracerebral hemorrhage (2.2 in 2005 and 2.5 in 2018, AAPC 0.6 [95% CI -1.0 to 2.3]) remained steady in younger adults. In older adults, rates of ischemic stroke and intracerebral hemorrhage declined, particularly in those ≥70 years of age. Rates of subarachnoid hemorrhage declined, but more so in younger than older adults. Stroke mortality declined over time in both age groups, attributable largely to declines in the mortality after severe strokes. Most trends were similar for men and women.

CONCLUSION

The incidence of ischemic stroke and intracerebral hemorrhage was steady in younger adults from 2005 to 2018, while it dropped in adults >70 years of age. Stroke mortality declined during this time.

Mortality Risk Among Heart Failure Patients With Depression: A Nationwide Population-Based Cohort Study

Background

The prevalence of depression is 4‐ to 5‐fold higher in heart failure patients than in the general population. We examined the influence of depression on all‐cause mortality in patients with heart failure.

Methods and Results

Using Danish medical registries, this nationwide population‐based cohort study included all patients with a first‐time hospitalization for heart failure (1995–2014). All‐cause mortality risks and 19‐year mortality rate ratios were estimated based on Cox regression analysis, adjusting for age, sex, time period, comorbidity, and socioeconomic status. The analysis included 9636 patients with and 194 887 patients without a diagnosis of depression. Compared with patients without a history of depression, those with depression had higher 1‐year (36% versus 33%) and 5‐year (68% versus 63%) mortality risks. Overall, the adjusted mortality rate ratio was 1.03 (95% CI 1.01–1.06). Compared with no depression, the adjusted mortality rate ratios for mild, moderate, and severe depression, as defined by diagnostic codes, were 1.06 (95% CI 1.00–1.13), 1.03 (95% CI 0.99–1.08), and 1.02 (95% CI 0.96–1.09), respectively. In a subcohort of patients, the mortality rate ratios were modified by left ventricular ejection fraction, with adjusted mortality rate ratios of 1.17 (95% CI, 1.05–1.31) for ≤35%, 0.98 (95% CI 0.81–1.18) for 36% to 49%, and 0.96 (95% CI 0.74–1.25) for ≥50%. Results were consistent after adjustment for alcohol abuse and smoking.

Conclusions

A history of depression was an adverse prognostic factor for all‐cause mortality in heart failure patients with left ventricular ejection fraction ≤35% but not for other heart failure patients.