Positive Predictive Value of Diagnostic Codes for Inflammatory Bowel Disease in the Danish National Patient Registry Among Individuals 50+ Years, Using Patient Records as Reference Standard

Figures & data

Figure 1 Flowchart.

Abbreviations: IBD, inflammatory bowel disease; NPR, the Danish National Patient Registry

Table 1 Baseline Characteristics of the 277 Participants Based on Information from the NPR

First NPR Diagnosis	IBD N=277 N(%)	CD N=61 N(%)	UC N=216 N(%)
Sex
Female	156 (56)	38 (62)	118 (55)
Male	121 (44)	23 (38)	98 (45)
Age at diagnosis^a
Median [Q1 + Q3]  Range		68 [64, 72] 57, 79	69 [64, 72] 53, 82
Patients with diagnostic codes referring to specific location in the gastrointestinal tract^b	126 (46)	19 (31)	108 (50)

Notes: ^aAge is missing from three patients. ^bK50.0, K50.0D, K50.1. K51.0, K51.1, K51.2, K51.2A, K51.3, K51.5, K518A.

Abbreviations: NPR, the Danish National Patient Registry; IBD, inflammatory bowel disease; CD, Crohn’s disease; UC, ulcerative colitis.

Table 2 Baseline Characteristics of the 277 Participants Based on Information from Patient Records

First Diagnosis in the Patient Records	Total N=277 N(%)	CD N=37 N(%)	UC N=120 N(%)	MC N=56 N(%)	IBDu N=4 N(%)	Other N=54 N(%)	Unknown N=6 N(%)
Sex
Female	156 (56)	27 (73)	47 (39)	48 (86)	2 (50)	27 (50)	5 (83)
Male	121 (44)	10 (27)	73 (61)	8 (14)	2 (50)	27 (50)	1 (17)
Location at diagnosis^a,b:	143 (52)	35 (95)	108 (90)
L1 ilieal		9 (26)
L2 colonic		18 (51)
L3 ileocolonic		6 (17)
L1+ L4		1 (3)
L2 + L4		1 (3)
E1 rectum			26 (24)
E2 left sided, distal			54 (50)
E3 extensive, pancolitis			28 (26)

Notes: L4: Isolated upper disease. ^aAccording to Montreal Classification. ^bExcluding 1 UC patient with the disease located to both sigmoid colon and ascending colon.

Abbreviations: CD, Crohn’s disease; UC, ulcerative colitis; MC, microscopic colitis; IBDu, undifferentiated inflammatory bowel disease.

Figure 2 Validity of diagnoses of IBD in the NPR among patients more than 50 years of age: review of 277 patient records.

Abbreviations: IBD, inflammatory bowel disease; NPR, the Danish National Patient Registry.

Table 3 Validity of the Diagnostic Codes for IBD, CD and UC in the NPR Using Number of Hospital Admissions/Out-Patient Clinic Visits with a Main Discharge Diagnosis Registered in the NPR as Criteria

	No. of Cases According to NPR	No. of Confirmed Cases in the Patient Record	No. of Cases Lost Compared to Using 1 Diagnosis as Criteria	PPV (95% CI)
Including MC as IBD case^a
At least one diagnosis of IBD  Female  Male	277 156 121	217 124 93	– – –	0.78 (0.73–0.83) 0.80 (0.72–0.86) 0.77 (0.68–0.84)
At least 2 diagnoses of IBD	157	141	76	0.90 (0.84–0.94)
At least 3 diagnoses of IBD  Female  Male	102 45 57	99 43 56	118 81 37	0.97 (0.92–0.99) 0.96 (0.85–1.00) 0.98 (0.91–1.00)
Excluding MC as case^b
At least one diagnosis of IBD  Female  Male	277 156 121	161 76 85	– – –	0.58 (0.52–0.64) 0.49 (0.41–0.57) 0.70 (0.61–0.78)
At least 2 diagnoses of IBD	157	123	38	0.78 (0.71–0.85)
At least 3 diagnoses of IBD  Female  Male	102 45 57	94 39 55	67 37 30	0.92 (0.85–0.97) 0.87 (0.73–0.95) 0.97 (0.88–1.00)
CD
At least one diagnosis of CD  Female  Male	61 38 23	31 23 8	– – –	0.51 (0.38–0.64) 0.61 (0.43–0.76) 0.35 (0.16–0.57)
At least 2 diagnoses of CD	37	24	7	0.65 (0.48–0.80)
At least 3 diagnoses of CD  Female  Male	28 18 10	21 15 6	10 8 2	0.75 (0.55–0.89) 0.83 (0.59–0.96) 0.60 (0.26–0.88)
UC
At least one diagnosis of UC  Female  Male	216 118 98	117 47 70	– – –	0.54 (0.47–0.61) 0.40 (0.31–0.49) 0.71 (0.61–0.80)
At least 2 diagnoses of UC	124	91	26	0.73 (0.65–0.81)
At least 3 diagnoses of UC  Female  Male	74 27 47	65 20 45	52 27 25	0.88 (0.78–0.94) 0.74 (0.54–0.89) 0.96 (0.86–0.99)

Notes: ^a Using patients with a diagnosis of CD, UC, IBDu and MC in the patient records as cases. ^b Using patients with a diagnosis of CD, UC and IBDu in the records as cases.

Abbreviations: IBD, inflammatory bowel disease; CD, Crohn’s disease; UC, ulcerative colitis; NPR, the Danish National Patient Registry; IBDu, undifferentiated IBD; MC, microscopic colitis; PPV, positive predictive value; CI, confidence interval.

Table 4 Validity of the Diagnostic Codes for IBD, CD and UC in the NPR Using Department Specialization as Criteria, Including Abdominal Surgical Departments as Specialized Departments of Gastroenterology

Diagnosis Department Specialization	No. of Cases According to NPR with at Least One Registration	No. of Confirmed Cases	PPV (95% CI)
Including MC as IBD case^a  Departments of internal medicine, surgery or gastroenterology Other/unknown	266	210	0.79 (0.74–0.84)
	11	7	0.64 (0.31–0.89)
Excluding MC as case^b  Departments of internal medicine, surgery or gastroenterology Other/unknown	266	154	0.58 (0.52–0.64)
	11	7	0.64 (0.31–0.89)
CD  Departments of internal medicine, surgery or gastroenterology Other/unknown	56	28	0.50 (0.36–0.64)
	5	3	0.60 (0.15–0.95)
UC  Departments of internal medicine, surgery or gastroenterology Other/unknown	210	113	0.54 (0.47–0.67)
	6	4	0.67 (0.22–0.96)

Notes: ^a Using patients with CD, UC, IBDu and MC in the patient records as cases.

^bUsing patients with CD, UC and IBDu in the records as cases.

Abbreviations: NPR, the Danish National Patient Registry; IBD, inflammatory bowel disease; CD, Crohn’s disease; UC, ulcerative colitis; IBDu, undifferentiated IBD; MC, microscopic colitis; PPV, positive predictive value; CI, confidence interval.