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, 24 (11), 659-67

The Swedish Personal Identity Number: Possibilities and Pitfalls in Healthcare and Medical Research


The Swedish Personal Identity Number: Possibilities and Pitfalls in Healthcare and Medical Research

Jonas F Ludvigsson et al. Eur J Epidemiol.


Swedish health care and national health registers are dependent on the presence of a unique identifier. This paper describes the Swedish personal identity number (PIN) and explores ethical issues of its use in medical research. A ten-digit-PIN is maintained by the National Tax Board for all individuals that have resided in Sweden since 1947. Until January 2008, an estimated 75,638 individuals have changed PIN. The most common reasons for change of PIN are incorrect recording of date of birth or sex among immigrants or newborns. Although uncommon, change of sex always leads to change of PIN since the PIN is sex-specific. The most common reasons for re-use of PIN (n = 15,887), is when immigrants are assigned a PIN that has previously been assigned to someone else. This is sometimes necessary since there is a shortage of certain PIN combinations referring to dates of birth in the 1950s and 1960s. Several ethical issues can be raised pro and con the use of PIN in medical research. The Swedish PIN is a useful tool for linkages between medical registers and allows for virtually 100% coverage of the Swedish health care system. We suggest that matching of registers through PIN and matching of national health registers without the explicit approval of the individual patient is to the benefit for both the individual patient and for society.


Fig. 1
Fig. 1
Calculation of the check digit of the PIN. Each digit in the PIN is multiplied by 2 or 1 in alternating fashion. The products are summed up, but products consisting of two digits (*) are first summed up themselves (i.e. 12 = 1 + 2 = 3). In this case, the sum of products treated this way, is 36. # The last digit in the product sum (in this case 6) is extracted from 10 (the difference being “4”). If the product sum ends with “0” (e.g. 10, 20, 30, 40 etc.), the check digit “0” is assigned since “10” cannot function as the check digit
Fig. 2
Fig. 2
Potential linkage between different registers involving patient identification from the National Board of Health and Welfare. ICD International Classification of Disease Code. (Used in the paper “A population-based study of coeliac disease, neurodegenerative and neuroinflammatory diseases” [9]). NBHW National Board of Health and Welfare. SS Statistics Sweden
Fig. 3
Fig. 3
Linkage of own data. * Data collected by the researcher. # Matched controls identified by Statistics Sweden (Box 1). SS Statistics Sweden (Statistiska Centralbyrån, SCB). NBHW National Board of Health and Welfare (Socialstyrelsen)

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