Background
History and coverage of the IPR
IPR variables
Variable | Description |
---|---|
Patient-related data | |
Personal Identity Number (PIN) | Combination of date of birth, three-digit birth number and a check digit [3]. Personal identity number shall be reported for all admissions/discharges, except for induced abortions where it is not registered for legal reasons |
Sex | 1 = male; 2 = female |
Age | Age in years at discharge. In individuals with missing birth dates, the difference between year of discharge and birth year is used to calculate age. |
County | The county where the patient has his/her permanent residence (this is not necessarily the county where the patient is admitted). |
Municipality and parish | Usually consists of six digits, where positions 1-2 indicate county, 3-4 municipality and 5-6 parish. Individuals living outside Sweden are assigned the value "99". Missing data have been replaced by data from Statistics Sweden. |
Data about caregiver (hospital/department)
| |
Hospital | Each hospital in Sweden has a unique 5-digit code assigned by the National Board of Health and Welfare (NBHW)(e.g., Lund University Hospital has code 41001). |
Type of department | Each type of department or health centre has a unique code assigned by the NBHW (e.g. ophthalmology departments have code 511) |
Administrative data
| |
Admission date | Year-month-day |
Discharge date | Year-month-day |
Duration of admission | Number of days at hospital. Patients discharged on the day of admission are assigned the value "1". |
Elective health care | 1 = Yes, 2 = No |
Mode of admission | 1 = from other hospital/department, 2 = from special living (e.g., home for disabled people, or geriatric care), 3 = other (i.e. from home) |
Mode of discharge | 1 = to other hospital/department, 2 = to special living (e.g., home for disabled people or geriatric care), 3 = other (i.e. discharged to home), 4 = deceased. |
Medical data
| |
Diagnoses | In 1964-1996, the IPR permitted up to 6 diagnoses per discharge. Between 1997-2009 8 diagnoses could be recorded (one of them being the primary diagnosis). |
Primary and additional diagnoses | The primary diagnosis or "main condition" should be the condition diagnosed at the end of the episode of health care responsible for the patient's need for treatment or investigation. The additional (secondary or contributory diagnoses/conditions) may or may not contribute to the primary diagnosis. They may be co-morbidities and/or complications. Since 2010 the number of possible additional diagnoses per case is unlimited (however, the NBHW will generally only deliver the first 7 additional diagnoses to researchers who request data from the IPR). |
External cause of injury or poisoning (E-code) - or "Chapter XX codes". | Until 1997, only one E-code could be recorded per discharge; from 1998, numerous "E-codes" may be recorded. With the introduction of ICD-10 in 1997, E-codes should be referred to as "Chapter XX-codes". (In ICD-10, E00-E99 codes represent metabolic conditions). |
Procedures | In 1964 the Swedish NBHW introduced a national classification of procedures based on an American classification of surgical procedures. It had four digit-codes (e.g. appendectomy 4510). Since 1997, a Swedish version of the NOMESCO Classification of Surgical Procedures is in use. This classification is based on five-character alpha-numeric codes (e.g. JEA01 for appendectomy). Current procedures are listed in the Swedish Classification of surgical and medical procedures (Swedish: "KVÅ" - klassifikation av vårdåtgärder)(issued by the NBHW). Between 1964 and 1996, up to 6 operations/surgical procedures could be listed per discharge. From 1997, up to 12 operations/surgical procedures could be listed per discharge. In the future it will be possible to record more than 12 diagnoses per discharge. Since 2007, all performed procedures are mandatory to record, including medical procedures. The surgeon may also (voluntarily) report date of operation and type of anaesthesia and drugs used according to the ATC list. |
Psychiatric care | 0 = voluntary care, 1-4: compulsory psychiatric inpatient care (under different conditions or according to certain laws). If a patient has been treated according to categories 1, 2, 3 or 4, the condition prevailing most of the time shall be reported. Compulsory care can be further divided into "forensic" and "civil", depending on the reasons for compulsory care. |
Personal identity number (PIN)
Primary diagnosis
Injuries and poisoning: external cause
Mode of admission and discharge
Alternative registers
Earlier assessment of the IPR
Disease/ Procedure | Quality Register | Total number of cases | Matching between the Quality Register and the Patient Register (%) | Proportion of all cases identified through the Patient Register (%) |
---|---|---|---|---|
Hernia surgery* | Swedish Hernia Register | 17,707 | 69.9 | 92.5 |
Cholecystectomy* | Swedish Register of Gallstone Surgery and ERCP | 12,472 | 79.9 | 96.4 |
ERCP* | 7,458 | 54.5 | 71.2 | |
Multiple Sclerosis* | Swedish Multiple Sclerosis Register | 13,503 | 52.9 | 76.4 |
Knee arthroplasty | The Swedish Knee Arthroplasty Register | 11,122 | 90.1 | 93.6 |
Hip arthroplasty | The Swedish Hip Arthroplasty Register | 14,757 | 91.0 | 93.4 |
Hip fracture | The Swedish Hip Fracture Register | 15,920 | 64.0 | 95.3 |
Surgery on the abdominal aorta* | Swedvasc | 1,784 | 77.4 | 90.6 |
Infrainguinal bypass surgery | 979 | 72.4 | 81.9 | |
Carotid artery surgery | 1,584 | 81.6 | 95.2 | |
First stroke | Swedish Stroke Register | 22,202 | 79.4 | 96.0 |
Heart surgery | Swedish Heart Surgery Register# | 13,440 | 95.1 | 97.6 |
Cataract surgery* | National Cataract Register | 75,050 | 75.2 | 78.6 |
Prostate cancer* | National Prostate Cancer Register | 3,985 | 62.0 | 82.8 |
Use of the IPR
Methods
Assessment by the current study
Diagnosis | Correct diagnosis in the IPR (%) = positive predictive value (PPV) | Comment | Main Author | PubMed ID | Year | Gold Standard (reference) |
---|---|---|---|---|---|---|
Cardiovascular disease | ||||||
Myocardial infarction | 36/36 (100) | Only primary diagnoses were evaluated. NPV = 861/864 (99.7) | Nilsson [7] | 8114596 | 1994 | MR |
Myocardial infarction | 2053/2101 (98) | Patients aged 45 - 70 years in 1992 - 1994. | Linnersjö[34] | 11121592 | 2000 | MR |
Angina Pectoris | 18/19 (95) | Only primary diagnoses were evaluated. NPV = 879/881 (99.8) | Nilsson [7] | 8114596 | 1994 | MR |
Heart failure (HF) | 259/317 (81.7) | Definition of HF proposed by the European Society of Cardiology [35]. Restricting the diagnosis HF to the primary diagnosis, then 133/140 (95.0%) were correct. | Ingelsson [36] | 15916919 | 2005 | ULSAM |
Heart failure | 15/17 (88) | Only primary diagnoses were evaluated. NPV = 876/883 (99.2) | Nilsson [7] | 8114596 | 1994 | MR |
Atrial fibrillation (using ICD-codes for atrial fibrillation or atrial flutter) | 97/100 (97) | 95 individuals had ECGs consistent with atrial fibrillation. Two patients had no ECGs available but were regarded as having atrial fibrillation on the basis of medical records. | Smith [37] | 19936945 | 2009 | MR + Electrocardiograms (ECG) |
Non-fatal strokes | 3492/5101 (68.5) | Patients aged 25-74 years in 1985-89. Criteria for acute stroke in this study were based on WHO criteria. | Stegmayr [38] | 1291884 | 1992 | MONICA-population based stroke register |
Stroke/Transient ischemic Attack | 207/210 (98.6) | ULSAM | Wiberg | (PC, Feb 12) | ULSAM | |
Gestational hypertension | 108/111 (97.3) | Zetterström | (PC, March 3) | MR | ||
Gestational hypertension | 97/115 (84.3) | Ros [39] | 9620050 | 1998 | MR | |
Vascular interventions (for lower limb ischemia) | 545/546 (99.8) | Hultgren [40] | 11170873 | 2001 | MR | |
Autoimmune/immune-mediated diseases
| ||||||
Rheumatoid arthritis (RA) | 489/510 (95.9) | Malmö, Sweden, 1990-1994. According to the RA criteria of the American College of Rheumatology [41]. | Turesson [42] | 10461483 | 1999 | MR |
Rheumatoid arthritis | Without lymphoma: 440/505 (87.1) With lymphoma: 386/413 (93.5) | In 40 of the 386 cases with lymphoma, medical records did not include enough information to evaluate whether the RA criteria of the American College of Rheumatology were fulfilled but all available information supported the diagnosis of RA | Baecklund [22] | 16508929 | 2006 | MR |
Wegener's granulomatosis | 68/78 (87) | American College of Rheumatology diagnostic criteria [43] | Knight [12] | 12115591 | 2002 | MR |
Celiac disease | 66/77 (86) of patients with later lymphoma | Only in 8 patients could celiac disease be ruled out. In 3 patients, the chart reviews were consistent with possible celiac disease. | Ekström-Smedby [44] | 15591504 | 2005 | MR |
Primary adrenocortical insufficiency | 105/133 (78.9) | Bensing [45] | 18727712 | 2008 | Patients tested positive for 21-OH autoantibodies | |
Diabetes mellitus (type 1 and 2)* | 22/28 (79) | Only primary diagnoses were evaluated. NPV = 872/872 (100) | Nilsson [7] | 8114596 | 1994 | MR |
Both diabetes (type 1 or 2) and foot ulcer* | 235/236 (99.6) admissions were correct with regards to ICD-coding | 117 patients with deep foot infections and type 1 or 2 diabetes, who had been referred to a multidisciplinary foot-care team at Lund University Hospital. | Ragnarson-Tennvall [46] | 11123504 | 2000 | MR |
Inflammatory bowel disease (IBD) | 4778/6440 (74) | 1965-1983. Due to the ICD-classification used at this time, ulcerative colitis could not be distinguished from Crohn's disease, and therefore "overall IBD" was evaluated | Ekbom [47] | 1985033 | 1991 | MR + histopathological reviews |
Psychiatric disease and neurology
| ||||||
Schizophrenia | 94/100 (94.9) | Review of medical records with structured diagnostic interviews | Ekholm [48] | 16316898 | 2005 | MR |
Schizophrenia | 78/91 (85.7) | Individuals born 1973-77. DSM-IV criteria for schizophrenia syndrome | Dalman [49] | 12395142 | 2002 | MR |
Schizophrenia | 106/111 (95.5) | Review of 121 consecutive cases in one city using a structured DSM-IV checklist, 111 records obtained | Hultman [50] | 16863597 | 2006 | MR |
Schizophrenia, schizophreniform disorder or schizoaffective disorder | 94/168 (56) | Primary diagnoses that fulfilled DSM-IV criteria (OPCRIT algorithm) | Reutfors [51] | - | 2009 | MR |
Schizophrenia † | 78/104 (75.0) to 85/104 (81.7) | 104 patients discharged in 1971 with a diagnosis of schizophrenia. DSMIII-criteria were used for this validation. From Stockholm County IPR. A strict review found a PPV of 75%. This figure increased to 85% when some lack of information was accepted (less strict criteria). | Kristjansson [52] | - | 1987 | MR |
Schizophrenia | (Kappa = 0.37 correlating to an agreement rate of 68%) | All individuals with a diagnosis of schizophrenia in the IPR and who had an inpatient forensic psychiatric assessment using a national register of all such evaluations from 1988-2000 (n = 1638). | Fazel [25] | 19454640 | 2009 | Forensic psychiatric assessment |
Schizophrenia | 34/44 (77%) | Bergman [53] | - | 1999 | Four-week- inpatient assessment in forensic psychiatry department | |
Alzheimer | 54/75 (72) | Jin [54] | 15326258 | 2004 | Clinical work-up following phone interview | |
Personality disorders | 37/40 (92) | Random sample of 40 individuals out of 401 violent offenders with personality disorders from a longitudinal study | Grann [55] | - | 1998 | MR |
Personality disorders | 30/55 (55%) | Bergman [53] | - | 1999 | Four-week- inpatient assessment in forensic psychiatry department | |
Guillain-Barré Syndrome (GBS) | 69/83 (83) | 83% of patients fulfilled the National Institute of Neurological and Communicative Disorders and Stroke criteria for GBS [56]. PPV of first primary diagnosis with GBS was 84%; and for secondary diagnosis 75%. | Jiang [57] | 7785420 | 1995 | MR |
Herpes simplex encephalit | 223/638 (35.0) | 1990-2001 | Hjalmarsson [58] | 17806053 | 2007 | Laboratory data (positive finding of HSV-1) |
Trauma and fractures
| ||||||
Brain concussion | 18/18 (100) | Only primary diagnoses were evaluated. NPV = 880/882 (99.8) | Nilsson [7] | 8114596 | 1994 | MR |
Hip fracture | 21/22 (95) | Only primary diagnoses were evaluated. NPV = 877/878 (99.9) | Nilsson [7] | 8114596 | 1994 | MR |
Hip fracture | 2556/2597 (98.4) | Cases derived both from IPR and operation registers. | Michaelsson [59] | 9632404 | 1998 | MR |
Injuries | 1299/1370 (94.8) | Injury code was correct at 3-digit-level. | Gedeborg | - | (PC, Feb 3) | MR |
Surgical procedures (and related medical conditions)
| ||||||
Major amputations (leg and arm) | 610/624 (97.8) | Unique number of amputations was 610 in 624 patients. | Malmstedt | (PC, Feb 24) | MR | |
Appendicitis† | 1661/1840 (90.3) | Performed in the Jönköping county. Incidental appendectomies were excluded. The IPR overestimated the prevalence of appendicitis with 6%. The negative predictive value of appendicitis was 94.0% and the accuracy 91.3%† | Andersson [60] | 8298378 | 1994 | Histological examination of excised tissue (in patients undergoing appendectomy) |
Inguinal hernia | 17/18 (94) | Only primary diagnoses were evaluated. NPV = 882/882 (100) | Nilsson [7] | 8114596 | 1994 | MR |
Other disorders
| ||||||
Achalasia | 67/83 (81) | Zendehdel [61] | 17488250 | 2007 | MR | |
Prostate hyperplasia | 14/14 (100) | Only primary diagnoses were evaluated. NPV = 882/886 (99.5) | Nilsson [7] | 8114596 | 1994 | MR |
Asthma | 14/15 (93) | Only primary diagnoses were evaluated. NPV = 885/885 (100) | Nilsson [7] | 8114596 | 1994 | MR |
Abdominal pain (observation for abdominal pain) | 33/37 (89) | Only primary diagnoses were evaluated. NPV = 860/863 (99.7) | Nilsson [7] | 8114596 | 1994 | MR |
Preeclampsia | 137/148 (92.6) | Ros [39] | 9620050 | 1998 | MR | |
Endometriosis | Without ovarial cancer: 615/628 (97.9% correct). With ovarial cancer: 220/225 (97.8% correct) | Melin | - | (PC, Feb 3) | MR | |
Foot ulcer (only) | 249/250 (99.6) admissions to hospital were correct with regards to ICD-coding | Based on 117 patients with deep foot infections and type 1 or 2 diabetes, referred to multidisciplinary foot-care team. Specificity for foot ulcers and concomitant diabetes was 98%. | Ragnarson-Tennvall [46] | 11123504 | 2000 | MR |
Connective tissue disease (CTD) | 71/91 (78%) | In this study CTD included rheumatoid arthritis, systemic lupus erythemathosus, sclerodermia, Sjögren's syndrome, dermatomyositis, polymyositis etc. | Nyren [62] | 9492663 | MR | |
Acute pancreatitis | 695/602 (98.8) | Among 602 patients with a primary or secondary diagnosis of acute pancreatitis in the IPR. 84.0% had a definitive acute pancreatitis and another 14.8% a probable acute pancreatitis. | Lindblad | (PC, Feb 6) | MR + laboratory tests and radiological imaging |
Diagnosis | Proportion identified through the IPR (%) (sensitivity) | Comment | Main Author | PubMed ID | Year | Gold Standard (Reference) |
---|---|---|---|---|---|---|
Cardiovascular disease | ||||||
Myocardial Infarction (MI) | 54/59 (91.5) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Myocardial infarction | 99/128 (77) | Merlo [63] | 10870938 | 2000 | Men born 1914 | |
Myocardial infarction | 113/144 (79) | Merlo [63] | 10870938 | 2000 | The Skaraborg Hypertension Study | |
Myocardial Infarction | 3201/4148 (77.2) | The researchers identified all MIs in Stockholm county in 1973 through the local IPR and the national Cause of Death Register (restricted to individuals living in Stockholm). | Ahlbom [64] | 721364 | 1978 | Swedish Cause of Death Register |
Myocardial infarction | 4746/5832 (81.4) of MI cases in community registers were found in IPR or the Cause of Death Register. | IPR and Cause of Death Register data from 1972-1981 for regions with IPR registers at the time. 81% of cases in community registers were found in IPR or Cause of Death Register. Meanwhile 85% of cases in IPR and the Cause of Death Register were found in Community registers (disregarding non-matching fatal cases). | Hammar [65] | 2066207 | 1991 | Community registers with myocardial infarctions |
Angina Pectoris | 86/196 (43.9) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Acute coronary syndrome (MI or unstable angina pectoris) | IPR from emergency department missed 2% of 218 patients with acute coronary syndrome. | Discharge diagnoses from emergency department, Lund University Hospital. | Forberg [66] | 18804783 | 2009 | MR. The study evaluates different methods to identify acute coronary syndrome in patients, using information not available in the IPR (e.g. ECG measurements). |
Non-specified ischemic heart disease | 44/206 (21.4) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Stroke (non-subarachnoidal hemorrhage) | 318/377 (84.4) | Data from a local stroke incidence study at the Örebro University Hospital. | Appelros | - | (PC, Feb 22) | Local stroke incidence study |
Non-fatal strokes | 3492/3732 (93.6) of all cases 3492/3562 (98.0) of estimated hospital cases | Patients aged 25-74 years in 1985-89. Criteria for acute stroke from MONICA study were comparable to WHO criteria. | Stegmayr [38] | 1291884 | 1992 | MONICA-population based stroke register |
Stroke | 75/79 (95) | Merlo [63] | 10870938 | 2000 | The Skaraborg Hypertension Study | |
Stroke | 76/81 (94) | Merlo [63] | 10870938 | 2000 | "Men born 1914" | |
Stroke | 384/456 (84.2) | First-time stroke. Restricted to the Lund county. | Hallström [67] | 17156265 | 2007 | * |
Stroke/Transient ischemic A. | 217/232 (93.5) | ULSAM. | Wiberg | - | (PC, Feb 12) | ULSAM |
Hypertension | 5,886/42,796 (13.7) | IPR data from the county Östergötland. | Wiréhn [68] | 17786807 | 2007 | County registers of primary health care, outpatient hospital care and inpatient care |
Hypertension | 74/838 (8.8) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Gestational hypertension | 108/166 (65.1) | Zetterström | - | (PC, March 3) | All pregnant women in Sweden have their blood pressure examined. | |
Lipid disorders | 19/186 (10.2) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Autoimmune/immune-mediated diseases
| ||||||
Rheumatoid arthritis (RA) | 489/1150 (42.5) | Malmö, Sweden, 1990-1994. According to the RA criteria of the American College of Rheumatology [41]. | Turesson [42] | 10461483 | 1999 | Data from all rheumatologists and general practictioners in Malmö city, 1997 |
Diabetes, type 1 and 2* | 92/394 (23.3) | Cross-sectional, 1-year retrospective study. ≥20 year-olds from Degerfors area. | Elo [14] | 19084244 | 2009 | Data were obtained from IPR, hospital-based outpatient care and primary health care |
Type 1 and type 2 diabetes mellitus * | 349/436 (80.0) patients with diabetes in "source 1" could be identified in the IPR | The researchers evaluated the presence of type 1 or type 2 diabetes among patients with atrial fibrillations at the Södersjukhuset Hospital. All but 8 patients in this validation had type 2 diabetes. | Friberg | - | (PC, Feb 8) | MR + biochemistry data + data on insulin or other medication against diabetes |
Type 1 and type 2 diabetes mellitus* | 4,348/18,134 (24.0) | IPR data from the county Östergötland. | Wiréhn [68] | 17786807 | 2007 | County registers of primary health care, outpatient hospital care and inpatient care |
Both type 1/2 diabetes and foot ulcer | 235/280 (83.9) admissions could be identified through the IPR | Based on 117 patients with deep foot infections and type 1 or 2 diabetes, referred to multidisciplinary foot-care team. Specificity for foot ulcers and concomitant diabetes was 98%. | Ragnarson- Tennvall [46] | 11123504 | 2000 | MR |
Infectious disease
| ||||||
CNS infection in intensive care | ICD-9: 21/22 (95.4) ICD-10: 21/28 (75.0) | Specificity was 99.6% (ICD-9) and 99.7% (ICD-10). IPR data obtained through both primary and secondary diagnoses. | Gedeborg [69] | 17208121 | 2007 | ICU database diagnoses as reference |
Pneumonia in intensive care | ICD-9: 89/185 (48.1) ICD-10: 116/221 (52.5) | Specificity was 95.9% (ICD-9) and 95.8% (ICD-10). IPR data obtained through both main and secondary diagnoses. Using only primary diagnoses for pneumonia the specificity increased slightly but the sensitivity decreased to 31.2% and 38.2% respectively. | Gedeborg [69] | 17208121 | 2007 | ICU database diagnoses as reference |
Sepsis in intensive care | ICD-9: 85/186 (45.7) ICD-10: 94/179 (52.5) | Specificity was 97.5% (ICD-9) and 92.6% (ICD-10). IPR data obtained through both main and secondary diagnoses. | Gedeborg [69] | 17208121 | 2007 | ICU database diagnoses as reference, with inclusion in sepsis trials (IST) as secondary reference |
Tuberculosis | 12/15 (80) | Evaluation in patients with concomitant rheumatoid arthritis | Askling [70] | 15986370 | 2005 | MR |
Other disorders
| ||||||
Carotid, infrainguinal bypass and aortic aneurysm (AAA) procedures | 10,861/11,638 (93.3) of patients identified through Swedvasc (Svenska kärlregistret) or the IPR could be identified in the IPR | (Swedvasc) started in 1987 and became nationwide 1994. In the paper by Troëng et al data on infraingunal and carotid bypass originated from 5 years (2000-2004), while data on aortic aneurysms originated from 1 year (2006). Divided the sensitivity figures were: Carotid 96.8%; Infrainguinal 92.3% and aortic aneurysm 88.9%. | Troëng [15] And by | 18851920 | 2008 | The Swedish Vascular Register (Swedvasc) |
Asthma | 1,377/18,451 (7.5) | IPR data from the county Östergötland. | Wiréhn [68] | 17786807 | 2007 | County registers of primary health care, outpatient hospital care and inpatient care |
Dementia | 23/87 (26) | Participants originated from the study "Aging in women and men: a longitudinal study of gender differences in health behaviour and health among the elderly (as part of the Swedish Twin Register). The specificity for dementia was 97% (399/411) | Dahl [71] | 18007116 | MR + memory test scores etc. | |
Dementia | 41.3% for prevalent cases and 42.3% for incident cases. | Participants originated from the study "Aging in women and men: a longitudinal study of gender differences in health behaviour and health among the elderly (as part of the Swedish Twin Register). The specificity for dementia was 97% (399/411) | Rizutto | (PC, May 14) | Comparison between cases detected in IPR with cases derived from the Kungsholmen (KP) and SNAC-K Projects [72] | |
Foot ulcer (only) | 249/280 (88.9%) of admissions could be identified through the IPR | Based on 117 patients with deep foot infections and type 1 or 2 diabetes, referred to multidisciplinary foot-care team. | Ragnarson- Tennvall [46] | 11123504 | 2000 | MR |
Chronic obstructive pulmonary disease | 1,290/4,812 (26.8) | IPR data from the county Östergötland. | Wiréhn [68] | 17786807 | 2007 | County registers of primary health care, outpatient hospital care and inpatient care |