Importance of Reporting Complete Procedures of Identifying Patients from the Danish National Patient Registry: The Case of Neonatal Jaundice and Epilepsy

Figures & data

Figure 1 Illustration of the data in the administrative table ^a(the 3rd section) and diagnostic table ^b(the 4th section) for 9 persons (each had a unique person’s identification number “pnr” and was marked with a color) including main variables ^c, diagnostic ICD codes ^d, and diagnostic types ^ein the Danish National Patient Registry using diagnosis of epilepsy as an example, and process in identifying patients with a diagnosis of epilepsy including categorization the diagnoses (a primary or secondary diagnosis ^f, a referral diagnosis ^g, and an associated diagnosis ^h) (the 5th section), groups of persons according to their diagnoses ^{i, j, k} (the 2nd section), and persons identified by approach 1^l and 2^m (the 1st section) ⁿ.

Notes: ^aThe administrative table contains one observation for one hospital contact with a unique ‘recnum’. ^bThe diagnostic table contains one or more observations related to one hospital contact. ^cLabel of variables. pnr: Person’s identification. recnum: Administrative record number of hospital contacts. c_adiag: Primary diagnosis of the hospital contact. c_diag: All diagnostic information including primary, secondary, referral diagnosis, and additional diagnostic information to the primary, secondary, referral diagnosis . c_diagtype: Type of diagnosis. c_tildiag: Additional diagnostic codes to the primary, secondary, referral diagnosis, if any. ^dDG40: G40 is the ICD 10 code for epilepsy, which is added a capital D in the data; DZ03: an example of Z-codes in the ICD 10 ranging from DZ00-DZ99. Dxxx: other codes besides codes for epilepsy and Z-codes. ^eValue of the variable ‘c_diagtype’ (type of diagnosis). A: Main / primary diagnosis. B: Auxiliary / secondary diagnosis. C: Complication. G: Basic diagnosis when the basic diagnosis is different from the main diagnosis. H: Referral diagnosis. +: indicates that the diagnosis in the variable ‘c_diag’ has an associated diagnosis and that the associated diagnosis is stated in the variable ‘c_tildiag’. ^fWe identified a primary or secondary diagnosis when the diagnostic observation with the variable ‘c_diag’ was coded with the codes of interest (epilepsy or jaundice), and the variable ‘c_diagtype’ was coded with ‘A, B, G, and C’. However, the number of observations with the value ‘G and C’ were few. ^gA referral diagnosis which was the diagnosis given by the referring physician or hospital / department as a reason for referral. ^hAn associated diagnosis which was originated from the additional codes to a primary, secondary, or referral diagnosis in the DNPR. ⁱGroup 1: persons who had a primary or secondary diagnosis and a referral or an associated diagnosis as well (person 1, 2, 3), ^jGroup 2: persons who had a primary or secondary diagnosis only (person 4, 5, 6). ^kGroup 3: persons with a referral or an associated diagnosis only (7,8, 9). ^lApproach 1: Procedures of identifying persons with a disease diagnosis, epilepsy as an example. 1. Link the administrative data with the diagnoses data. 2. Identify all records if the variable ‘c_diag’ or ‘c_tildiag’ contained the code of interest for the diagnosis, DG40-DG41 for epilepsy. 3. Exclude records for the referral diagnosis if the variable ‘c_diagtype’ was coded with ‘H’. ^mApproach 2: Procedures of identifying persons with a disease diagnosis, epilepsy as an example. 1. Exclude hospital contacts if the variable ‘c_adiag’ was coded with Z00 – Z99. 2. Link the administrative data with the diagnoses data. 3. Identify all records if the variable ‘c_diag’ or ‘c_tildiag’ contained the code of interest for the diagnosis, DG40-DG41 for epilepsy. 4. Exclude records for the referral diagnosis if the variable ‘c_diagtype’ was coded with ‘H’.. 5. Exclude records if the variable ‘c_diag’ was coded with Z00 – Z99. ⁿApproach 1 identified person 1, 2, 3, 4, 5, 6, 8, and 9 with a diagnosis of epilepsy excepting person 7. Approach 2 identified person 1, 2, 3, 4, 5, 9 with a diagnosis of epilepsy excepting for person 6, 7, 8.

Table 1 Summary of Persons with a Hospital Contact Related to Neonatal Jaundice and Summary of Approach 1 and Approach 2 in Identifying Persons with a Diagnosis of Neonatal Jaundice Among the Study Population of Singletons Born Between 01 Jan 1997 and 30 Nov 1996 in Denmark (N=1,186,683)

	All		Approach 1		Approach 2
	Number	%	Number	%	Number	%
Persons with at least one hospital contact related to neonatal jaundice	65,938	5.6
Persons with a diagnosis of neonatal jaundice according to the approach			65,736	5.5	45,928	3.9
			Identifying persons in group 1, 2, and 3 by the approach (numbers in the brackets are persons excluded by the approach)
Categorization of persons according to their diagnostic observations	Number	Col %	Number	Row %	Number	Row %
Group 1: persons with a primary or secondary diagnosis and a referral or an associated diagnosis of neonatal jaundice as well	4964	7.5	4964	100.0	4667	94.0
Group2: persons with a primary or secondary diagnosis of neonatal jaundice only	53,527	81.2	53,527	100.0	41,201	77.0
Group 3: persons with a referral or an associated diagnosis of neonatal jaundice only	7447	11.3	7245 (202)	97.3 (2.7)	60 (7387)	0.8 (99.2)

Table 2 Summary of Persons with a Hospital Contact Related to Epilepsy and Summary of Approach 1 and Approach 2 in Identifying Persons with a Diagnosis of Epilepsy Among the Study Population of Singletons Born Between 01 Jan 1997 and 30 Nov 1996 in Denmark (N=1,183,273^a)

	All		Approach 1		Approach 2
	Number	%	Number	%	Number	%
Persons with at least one hospital contact related to epilepsy	19,486	1.7
Persons with a diagnosis of epilepsy according to the approach			14,604	1.2	10,441	0.9
			Identifying persons in group 1, 2, and 3 by the approach (numbers in the brackets are persons excluded by the approach)
Categorization of persons according to their diagnostic observations	Number	Col %	Number	Row %	Number	Row %
Group 1: persons with a primary or secondary diagnosis and a referral or an associated diagnosis of epilepsy as well	6925	35.5	6925	100.0	6722	97.1
Group2: persons with a primary or secondary diagnosis of epilepsy only	4011	20.6	4011	100.0	3693	92.1
Group 3: persons with a referral or an associated diagnosis of epilepsy only	8550	43.9	3668 (4882)	42.9 (57.1)	26 (8524)	0.3 (99.7)

Notes: ^aChildren who died or emigrated during the neonatal period (the first 28 days after birth) were excluded (n=3410).