Use of existing data sources in clinical epidemiology: Finnish health care registers in Alzheimer’s disease research – the Medication use among persons with Alzheimer’s disease (MEDALZ-2005) study

Figures & data

Figure 1 Cohort formation.

Notes: The participants were identified from the special reimbursement register and SII benefits database of 2005 and the data from separate registers were retrieved by the register maintainers.
Abbreviations: AD, Alzheimer’s disease; DR, discharge register; MEDALZ-2005, MEDication use among persons with ALZheimer’s disease; NIHW, National Institute of Health and Welfare; PIN, personal identification number; SII, Social Insurance Institution.

Table 1 MEDALZ-2005 data sources and their contents

Register	Data provided
Prescription register^Citation9	All reimbursed medicines, emollient cream, and clinical nutrients purchased by the individual. Medicines used in hospitals are not included, but the register covers prescriptions written by hospital physicians and dispensed in community settings. For each medicine, the prescription register contains data on dispensing date, number of packages/tablets, strength of the medicine, defined daily dose, and cost of medication.
Reimbursement register^Citation13	Entitlement to special reimbursement due to severe chronic diseases such as Alzheimer’s disease, diabetes, psychosis, epilepsy, glaucoma, rheumatic conditions, asthma, chronic obstructive pulmonary disease, hypothyreosis and several cardiovascular diseases, including cardiac insufficiency, chronic hypertension, and chronic ischemic heart diseases. To be included in the Special Reimbursement Register, the diagnosis must be based on explicit predefined criteria and written documentary evidence, including results of diagnostic tests such as imaging or blood biochemistry, which must be provided to the SII by a physician.
Hospital discharge register^Citation53	Use of in- and outpatient health care services. The diagnoses for each admission are made by the attending physician. The register contains the following information on each hospital visit: dates; reason for hospital stay (up to six ICD codes per visit; versions ICD8, 9, and 10); specialty of the caring unit; date of surgery; up to five operational codes (NOMESCO classification); where the patient was discharged to; and an assessment of need for assistance in activities of daily life. In addition, for patients admitted to a psychiatric unit, data are available on whether treatment was involuntary, duration of involuntary treatment, recurrence of visits to the psychiatric unit, and use of restrictive methods.
Discharge register from social institutions^Citation25	Home care and care in social service institutions, including dates, reason for admission, status of independence when discharged, and where the client was discharged to.
Cancer register^Citation24	All malignant neoplasms, carcinoid tumors, carcinoma in situ lesions (except those of the skin), cervical intraepithelial neoplasia grade III, histologically benign tumors of the central nervous system and meninges, transitional cell papillomas of the urinary tract, and ovarian tumors with borderline malignancy. Each cancer considered to be an independent new primary lesion is registered separately and all independent cancer processes are coded as separate entities. Data on diagnosis date, primary site, basis of diagnosis, localization stage, malignancy, histology/cell type, treatment details, and survival are included.
Statistics Finland^Citation11	Causes of death.

Abbreviations: ICD, International Classification of Diseases; NOMESCO, Nordic Medico-Statistical Committee; SII, Social Insurance Institution; MEDALZ-2005, MEDication use among persons with ALZheimer’s disease.

Table 2 Description of the study population at baseline (December 31, 2005)

	AD group n = 27,948	Non-AD group n = 27,948
Age in 2005, years	80.6 (6.8)	80.6 (6.8)
Sex
Men	9,014 (32.3)	9,014 (32.3)
Women	18,934 (67.7)	18,934 (67.7)
History of comorbidities
Cardiovascular disease	14,194 (50.80)	14,544 (52.0)
Diabetes	3,355 (12.0)	2,993 (10.7)
Asthma/chronic obstructive pulmonary disease	2,045 (7.3)	2,404 (8.6)
Epilepsy	577 (2.1)	351 (1.3)
Modified Charlson comorbidity indexa
0	16,075 (57.5)	16,152 (57.8)
1	7,575 (27.1)	7,678 (27.5)
2	3,177 (11.4)	3,103 (11.1)
≥3	1,121 (4.0)	1,015 (3.6)
Year of AD diagnosis
1999	724 (2.6)	NA
2000	1,146 (4.1)	NA
2001	2,010 (7.2)	NA
2002	3,302 (11.8)	NA
2003	5,904 (21.1)	NA
2004	7,678 (27.5)	NA
2005	7,184 (25.8)	NA
Medication use in 2005
Any antipsychotic (ATC code N05A)	6,167 (22.1)	1,216 (4.4)
Anti-dementia medications (ATC code N06D)	23,979 (85.8)	0
Any antiepileptic medication (ATC code N03A)	1,412 (5.1)	953 (3.4)
Any opioids (ATC code N02A)	997 (3.6)	1,291 (4.6)

Notes: Data are given as mean (SD) for age and n (%) for categorical variables. Those 145 persons without AD who had temporarily been entitled to reimbursed AD medication before 2006, together with their matched pair, are excluded.

a Includes the following diseases with corresponding scores: heart failure; coronary artery disease; type 1 or 2 diabetes; chronic asthma or chronic obstructive pulmonary disease; disseminated connective tissue diseases; rheumatoid arthritis and other comparable conditions (score of 1); uremia requiring dialysis; severe anemia in connection with chronic renal failure; and leukemia or other malignant diseases of blood and bone marrow including malignant diseases of the lymphatic system and all cancers (score of 2).

Abbreviations: AD, Alzheimer’s disease; ATC, Anatomical Therapeutic Chemical; SD, standard deviation.

Table 3 Differences between MEDALZ-2005 participants who died during 2006–2009 and survivors

	Alive in 2009 n = 37,639	Died during 2006–2009 n = 18,257
Age in 2005, years	79.4 (6.7)	83.2 (6.3)
Sex
Men	11,140 (29.6) [61.8]	6,888 (37.7) [38.2]
Women	26,499 (70.4) [70.0]	11,369 (62.3) [30.0]
AD	16,280 (43.3) [58.3]	11,668 (63.9) [41.7]
Cardiovascular disease	18,106 (48.1) [63.0]	10,632 (58.2) [37.0]
Diabetes	3,696 (9.8) [58.2]	2,652 (14.5) [41.8]
Asthma/chronic obstructive pulmonary disease	2,884 (7.7) [64.8]	1,565 (8.6) [35.2]
Epilepsy	533 (1.4) [57.4]	395(2.2) [42.6]
Year of AD diagnosis
1999	371 (2.28) [51.2]	353 (3.0) [48.8]
2000	622 (3.8) [54.3]	524 (4.5) [45.7]
2001	1,096 (6.7) [54.5]	914 (7.8) [45.5]
2002	1,837 (11.3) [55.6]	1,465 (12.6) [44.4]
2003	3,373 (20.7) [57.1]	2,531 (21.7) [42.9]
2004	4,456 (27.4) [58.0]	3,222 (27.6) [42.0]
2005	4,525 (27.8) [63.0]	2,659 (22.8) [37.0]
Modified Charlson comorbidity indexa
0	23,289 (61.9) [72.3]	8,938 (49.0) [27.7]
1	9,790 (26.0) [64.2]	5,463 (29.9) [35.8]
2	3,517 (9.3) [56.0]	2,763 (15.1) [44.0]
≥3	1,043 (2.8) [48.8]	1,093 (6.0) [51.2]

Notes: Data are given as mean (SD) for continuous variables and n (column percentage) [row percentage] for categorical variables. Those 145 persons without AD who had temporarily been entitled to reimbursed AD medication before 2006, together with their matched pair, are excluded.

a Includes the following diseases with corresponding scores: heart failure; coronary artery disease; type 1 or 2 diabetes; chronic asthma or chronic obstructive pulmonary disease; disseminated connective tissue diseases; rheumatoid arthritis and other comparable conditions (score of 1); uremia requiring dialysis; severe anemia in connection with chronic renal failure; and leukemia or other malignant diseases of blood and bone marrow including malignant diseases of the lymphatic system and all cancers (score of 2).

Abbreviations: AD, Alzheimer’s disease; MEDALZ-2005, MEDication use among persons with ALZheimer’s disease; SD, standard deviation.

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