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      External review and validation of the Swedish national inpatient register

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          Abstract

          Background

          The Swedish National Inpatient Register (IPR), also called the Hospital Discharge Register, is a principal source of data for numerous research projects. The IPR is part of the National Patient Register. The Swedish IPR was launched in 1964 (psychiatric diagnoses from 1973) but complete coverage did not begin until 1987. Currently, more than 99% of all somatic (including surgery) and psychiatric hospital discharges are registered in the IPR. A previous validation of the IPR by the National Board of Health and Welfare showed that 85-95% of all diagnoses in the IPR are valid. The current paper describes the history, structure, coverage and quality of the Swedish IPR.

          Methods and results

          In January 2010, we searched the medical databases, Medline and HighWire, using the search algorithm "validat* (inpatient or hospital discharge) Sweden". We also contacted 218 members of the Swedish Society of Epidemiology and an additional 201 medical researchers to identify papers that had validated the IPR. In total, 132 papers were reviewed. The positive predictive value (PPV) was found to differ between diagnoses in the IPR, but is generally 85-95%.

          Conclusions

          In conclusion, the validity of the Swedish IPR is high for many but not all diagnoses. The long follow-up makes the register particularly suitable for large-scale population-based research, but for certain research areas the use of other health registers, such as the Swedish Cancer Register, may be more suitable.

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          Most cited references49

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          The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis.

          The revised criteria for the classification of rheumatoid arthritis (RA) were formulated from a computerized analysis of 262 contemporary, consecutively studied patients with RA and 262 control subjects with rheumatic diseases other than RA (non-RA). The new criteria are as follows: 1) morning stiffness in and around joints lasting at least 1 hour before maximal improvement; 2) soft tissue swelling (arthritis) of 3 or more joint areas observed by a physician; 3) swelling (arthritis) of the proximal interphalangeal, metacarpophalangeal, or wrist joints; 4) symmetric swelling (arthritis); 5) rheumatoid nodules; 6) the presence of rheumatoid factor; and 7) radiographic erosions and/or periarticular osteopenia in hand and/or wrist joints. Criteria 1 through 4 must have been present for at least 6 weeks. Rheumatoid arthritis is defined by the presence of 4 or more criteria, and no further qualifications (classic, definite, or probable) or list of exclusions are required. In addition, a "classification tree" schema is presented which performs equally as well as the traditional (4 of 7) format. The new criteria demonstrated 91-94% sensitivity and 89% specificity for RA when compared with non-RA rheumatic disease control subjects.
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            Association of chronic inflammation, not its treatment, with increased lymphoma risk in rheumatoid arthritis.

            Chronic inflammatory conditions such as rheumatoid arthritis (RA) have been associated with malignant lymphomas. This study was undertaken to investigate which patients are at highest risk, and whether antirheumatic treatment is hazardous or protective. We performed a matched case-control study of 378 consecutive Swedish RA patients in whom malignant lymphoma occurred between 1964 and 1995 (from a population-based RA cohort of 74,651 RA patients), and 378 controls. Information on disease characteristics and treatment from onset of RA until lymphoma diagnosis was abstracted from medical records. Lymphoma specimens were reclassified and tested for Epstein-Barr virus (EBV). Relative risks (odds ratios [ORs]) for lymphomas (by subtype) associated with deciles of cumulative disease activity were assessed, as were ORs associated with drug treatments. The relative risks of lymphoma were only modestly elevated up to the seventh decile of cumulative disease activity. Thereafter, the relative risk increased dramatically (OR ninth decile 9.4 [95% confidence interval 3.1-28.0], OR tenth decile 61.6 [95% confidence interval 21.0-181.0]). Most lymphomas (48%) were of the diffuse large B cell type, but other lymphoma subtypes also displayed an association with cumulative disease activity. Standard nonbiologic treatments did not increase lymphoma risk. EBV was present in 12% of lymphomas. Risk of lymphoma is substantially increased in a subset of patients with RA, those with very severe disease. High inflammatory activity, rather than its treatment, is a major risk determinant.
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              Schizophrenia, substance abuse, and violent crime.

              Persons with schizophrenia are thought to be at increased risk of committing violent crime 4 to 6 times the level of general population individuals without this disorder. However, risk estimates vary substantially across studies, and considerable uncertainty exists as to what mediates this elevated risk. Despite this uncertainty, current guidelines recommend that violence risk assessment should be conducted for all patients with schizophrenia. To determine the risk of violent crime among patients diagnosed as having schizophrenia and the role of substance abuse in mediating this risk. Longitudinal designs were used to link data from nationwide Swedish registers of hospital admissions and criminal convictions in 1973-2006. Risk of violent crime in patients after diagnosis of schizophrenia (n = 8003) was compared with that among general population controls (n = 80 025). Potential confounders (age, sex, income, and marital and immigrant status) and mediators (substance abuse comorbidity) were measured at baseline. To study familial confounding, we also investigated risk of violence among unaffected siblings (n = 8123) of patients with schizophrenia. Information on treatment was not available. Violent crime (any criminal conviction for homicide, assault, robbery, arson, any sexual offense, illegal threats, or intimidation). In patients with schizophrenia, 1054 (13.2%) had at least 1 violent offense compared with 4276 (5.3%) of general population controls (adjusted odds ratio [OR], 2.0; 95% confidence interval [CI], 1.8-2.2). The risk was mostly confined to patients with substance abuse comorbidity (of whom 27.6% committed an offense), yielding an increased risk of violent crime among such patients (adjusted OR, 4.4; 95% CI, 3.9-5.0), whereas the risk increase was small in schizophrenia patients without substance abuse comorbidity (8.5% of whom had at least 1 violent offense; adjusted OR, 1.2; 95% CI, 1.1-1.4; P<.001 for interaction). The risk increase among those with substance abuse comorbidity was significantly less pronounced when unaffected siblings were used as controls (28.3% of those with schizophrenia had a violent offense compared with 17.9% of their unaffected siblings; adjusted OR, 1.8; 95% CI, 1.4-2.4; P<.001 for interaction), suggesting significant familial (genetic or early environmental) confounding of the association between schizophrenia and violence. Schizophrenia was associated with an increased risk of violent crime in this longitudinal study. This association was attenuated by adjustment for substance abuse, suggesting a mediating effect. The role of risk assessment, management, and treatment in individuals with comorbidity needs further examination.

                Author and article information

                Journal
                BMC Public Health
                BMC Public Health
                BioMed Central
                1471-2458
                2011
                9 June 2011
                : 11
                : 450
                Affiliations
                [1 ]Department of Paediatrics, Örebro University Hospital, Sweden
                [2 ]Clinical Epidemiology Unit, Department of Medicine, Karolinska University Hospital, Karolinska Institutet, Sweden
                [3 ]Section of Occupational and Environmental Medicine, University of Gothenburg, Sweden
                [4 ]Institute of Environmental Medicine, Karolinska Institutet, Sweden
                [5 ]Research Unit, Jämtland County, Sweden
                [6 ]Department of Public Health and Clinical Medicine, Umeå University, Sweden
                [7 ]Department of Statistics and Analyses, National Board of Health and Welfare, Stockholm, Sweden
                Article
                1471-2458-11-450
                10.1186/1471-2458-11-450
                3142234
                21658213
                b1f15eb2-c684-4e57-b945-1a7c87af489e
                Copyright ©2011 Ludvigsson et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 2 September 2010
                : 9 June 2011
                Categories
                Correspondence

                Public health
                register,disease,epidemiology,classification of diseases,morbidity
                Public health
                register, disease, epidemiology, classification of diseases, morbidity

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