Positive predictive value of first-time rheumatoid arthritis diagnoses and their serological subtypes in the Danish National Patient Registry

Figures & data

Table 1 Characteristics of first-time rheumatoid arthritis diagnoses recorded in the Danish National Patient Registry among participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals

Characteristics
Registered at least once with rheumatoid arthritis diagnosis during 1977–2016, n	331
Female, % (n)	70 (231)
Mean age, years (range)	65 (35–83)
Calendar periods, % (n)
1977–1987	6 (19)
1988–2010	70 (232)
2011–2016	24 (80)
Department type, % (n)
Rheumatology	58 (192)
Internal medicine	20 (65)
Surgery	16 (54)
Other	6 (20)
Patient type, % (n)
Inpatient	40 (134)
Outpatient	57 (189)
Other	3 (8)
Diagnosis type, % (n)
Main (A-diagnosis)	78 (257)
Secondary (B-diagnosis)	22 (74)
ICD-8 codes, % (n)	11 (37)
ICD-10 codes, % (n)a	89 (294)
M05, % (n)	45 (150)
M06, % (n)	44 (144)
ICD codes by patients’ gender
Men, n	100
ICD-8 codes, % (n)	12 (12)
ICD-10 M05 codes, % (n)	49 (49)
ICD-10 M06 codes, % (n)	39 (39)
Women, n	231
ICD-8 codes, % (n)	11 (25)
ICD-10 M05 codes, % (n)	44 (101)
ICD-10 M06 codes, % (n)	45 (105)
ICD-10 codes by patients age at the time of rheumatoid arthritis diagnosis registration
M05, n	150
<50 years, % (n)	1 (2)
50–59 years, % (n)	22 (33)
60–69 years, % (n)	44 (65)
>70 years, % (n)	33 (50)
M06, n	144
<50 years, % (n)	1 (2)
50–59 years, % (n)	13 (19)
60–69 years, % (n)	46 (66)
>70 years, % (n)	40 (57)

Note:

a ICD-10 code M05 – seropositive rheumatoid arthritis, ICD-10 code M06 – other rheumatoid arthritis.

Abbreviation: ICD, International Classification of Diseases.

Table 2 The positive predictive values of first-time overall rheumatoid arthritis diagnoses recorded in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals

Characteristics	Rheumatoid arthritisa			Rheumatoid arthritis + sDMARDb
	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)
Overall	205	331	61.9 (56.6–67.0)	185	211	87.7 (82.5–91.5)
Gender
Men	61	100	61.0 (51.0–70.2)	55	63	87.3 (76.2–93.7)
Women	144	231	62.3 (55.9–68.4)	130	148	87.8 (81.4–92.2)
Agec (years)
<50	13	19	68.4 (42.8–86.3)	10	11	90.1 (46.3–99.2)
50–59	49	72	68.1 (56.2–78.0)	44	50	88.0 (75.2–94.7)
60–69	76	133	57.1 (48.5–65.4)	68	82	82.9 (73.0–89.7)
>70	67	107	62.6 (52.9–71.4)	63	68	92.7 (83.2–97.0)
Department type
Rheumatology	138	192	71.9 (65.0–77.8)	128	142	90.1 (84.0–94.1)
Internal medicine	38	65	58.5 (45.9–70.0)	33	39	84.6 (68.9–93.2)
Other	29	74	39.2 (28.6–51.0)	24	30	80.0 (60.8–91.2)
Patient type
Inpatient	86	134	64.2 (55.6–71.9)	77	84	91.7 (83.3–96.0)
Outpatient	115	189	60.9 (53.7–67.6)	104	123	84.6 (76.9–90.0)
Other	4	8	50.0 (14.3–85.7)	4	4	100
Diagnosis type
Main (A-diagnosis)	175	257	68.1 (62.1–73.5)	160	181	88.4 (82.8–92.3)
Secondary (B-diagnosis)	30	74	40.5 (29.8–52.3)	25	30	83.3 (64.3–93.3)
Calendar periods
1977–1987	13	19	68.4 (42.8–86.3)	10	12	83.3 (45.7–96.7)
1988–2010	144	232	62.1 (55.6–68.1)	131	149	87.9 (81.6–92.3)
2011–2016	48	80	60.0 (48.7–70.3)	44	50	88.0 (75.2–94.7)
ICD-8 codes	29	37	78.4 (61.5–89.2)	25	27	92.6 (72.8–98.3)
ICD-10 codesd
M05	108	150	72.0 (64.2–78.7)	102	111	92.0 (85.0–95.8)
M06	68	144	47.2 (39.1–55.5)	58	73	79.5 (68.4–87.4)

Notes:

a Patients with first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry;

b patients with first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry who subsequently, at least once, redeemed a prescription for a sDMARD;

c patients’ age at the time of rheumatoid arthritis diagnosis registration;

d ICD-10 code M05 – seropositive rheumatoid arthritis, ICD-10 code M06 – other rheumatoid arthritis.

Abbreviations: ICD, International Classification of Diseases; sDMARD, synthetic disease-modifying antirheumatic drug.

Table 3 Positive predictive values of first-time rheumatoid arthritis diagnoses according to serological subtypes registered in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals, overall and by age groups at the time of rheumatoid arthritis diagnosis

First-time diagnosis in the Danish National Patient Registry, ICD-10 codes	Rheumatoid arthritisa			Rheumatoid arthritis + sDMARDb
	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)
M05 – seropositive rheumatoid arthritis	93	150	62.0 (53.9–69.5)	89	111	80.2 (71.6–86.7)
<50 yearsc	2	2	100d	2	2	100
50–59 yearsc	26	33	78.8 (60.6–90.0)	24	28	85.7 (66.0–94.9)
60–69 yearsc	34	65	52.3 (40.0–64.4)	33	43	76.7 (61.2–87.3)
>70 yearsc	31	50	62.0 (47.5–74.7)	30	38	79.0 (62.4–89.5)
M06 – other rheumatoid arthritis	36	144	25.0 (18.5–32.8)	30	73	41.1 (30.2–52.9)
<50 yearsc	1	2	50d	0	0	0
50–59 yearsc	1	19	5.3 (0.6–33.8)	0	6	0
60–69 yearsc	15	66	22.7 (14.0–34.7)	12	37	32.4 (18.9–49.7)
>70 yearsc	19	57	33.3 (22.1–46.9)	18	30	60.0 (40.9–76.5)

Notes:

a Patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry;

b patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry who subsequently, at least once, redeemed a prescription for a sDMARD;

c patients’ age at the time of rheumatoid arthritis diagnosis registration.

d Stata did not provide 95% CI in this case.

Abbreviations: ICD, International Classification of Diseases; sDMARD, synthetic disease-modifying antirheumatic drug.

Table 4 Positive predictive values of first-time rheumatoid arthritis diagnoses according to serological subtypes registered in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals by gender

First-time diagnosis in the Danish National Patient Registry, ICD-10 codes	Rheumatoid arthritisa			Rheumatoid arthritis + sDMARDb
	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)
Men
M05 – seropositive rheumatoid arthritis	29	49	59.2 (44.6–72.3)	27	35	77.1 (59.5–88.6)
M06 – other rheumatoid arthritis	11	39	28.2 (15.9–44.9)	9	20	45.0 (23.8–68.2)
Women
M05 – seropositive rheumatoid arthritis	64	101	63.4 (53.4–72.3)	62	76	81.6 (71.0–88.9)
M06 – other rheumatoid arthritis	25	105	23.8 (16.5–33.0)	21	53	39.6 (27.1–53.7)

Notes:

a Patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry;

b patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry who subsequently, at least once, redeemed a prescription for a sDMARD.

Abbreviations: ICD, International Classification of Diseases; sDMARD, synthetic disease-modifying antirheumatic drug.

Table 5 Positive predictive values of first-time rheumatoid arthritis diagnoses according to serological subtypes registered in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals by calendar periods

First-time diagnosis in the Danish National Patient Registry, ICD-10 codes	Rheumatoid arthritisa			Rheumatoid arthritis + sDMARDb
	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)	Confirmed rheumatoid arthritis, n	Registered rheumatoid arthritis, n	Positive predictive value % (95% CI)
M05 – seropositive rheumatoid arthritis
1988–2010	71	115	61.7 (52.4–70.3)	68	84	81.0 (70.9–88.1)
2011–2016	22	35	62.9 (45.1–77.7)	21	27	77.8 (57.0–90.2)
M06 – other rheumatoid arthritis
1988–2010	18	99	18.2 (11.7–27.2)	13	50	26.0 (15.4–40.3)
2011–2016	18	45	40.0 (26.4–55.4)	17	23	73.9 (50.9–88.6)

Notes:

a Patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry;

b patients with the first-time ever rheumatoid arthritis diagnosis registration in the Danish National Patient Registry who subsequently, at least once, redeemed a prescription for a sDMARD.

Abbreviations: ICD, International Classification of Diseases; sDMARD, synthetic disease-modifying antirheumatic drug.

Table 6 The most likely alternative diagnoses among patients, first-time registered with rheumatoid arthritis diagnosis in the Danish National Patient Registry during 1977–2016, but not confirmed by reviewing medical records

Alternative diagnoses	Number of nonconfirmed cases
Total number of nonconfirmed cases	106
Osteoarthritis	29% (n=31)
PMR or PMR with giant cell arteritis	9% (n=10)
Crystal arthropathy	9% (n=10)
Psoriatic arthritis	8% (n=9)
Connective tissue diseases	5% (n=5)
Tenosynovitis	3% (n=3)
Seronegative oligoarthritis	2% (n=2)
Enteropathic arthritis	1% (n=1)
Reactive arthritis	1% (n=1)
Juvenile idiopathic arthritis	1% (n=1)
Rotator cuff syndrome	1% (n=1)
Subacromial bursitis	1% (n=1)
Dupuytren’s contracture	1% (n=1)
Arthralgia	1% (n=1)
Joint cyst	1% (n=1)
Myalgia	1% (n=1)
Unknown	26% (n=27)

Abbreviation: PMR, polymyalgia rheumatica.

Figure S1 Serological status among confirmed RA diagnoses with available blood test results on IgM RF and/or ACPA before, at or within 1 month after the first-time registration in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals.

Notes: ^aRegistered with the ICD-8 code “712.39” (Arthritis rheumatoides alia et non specificata) at their first registration in the Danish National Patient Registry. ^bRegistered with one of ICD-10 “M05” (seropositive RA) codes at their first registration in the Danish National Patient Registry. ^cRegistered with one of ICD-10 “M06” (other RA) codes at their first registration in the Danish National Patient Registry.

Abbreviations: ACPA, anti-citrullinated protein antibody; ICD, International Classification of Diseases; IgM RF, immunoglobulin M rheumatoid factor; RA, rheumatoid arthritis.

Table S1 The blood test results of IgM RF and ACPA among confirmed ICD-10 M05 (seropositive) RA diagnoses in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals

Confirmed ICD-10 M05 diagnoses, n=108	IgM RFa
ACPAa		Positive, % (n)	Negative, % (n)	Not available, % (n)	Overall, % (n)
	Positive, % (n)	25 (27)	0	0	25 (27)
	Negative, % (n)	4.6 (5)	0.9 (1)	0	5.6 (6)
	Not available, % (n)	56.5 (61)	6.5 (7)	6.5 (7)	69.4 (75)
	Overall, % (n)	86.1 (93)	7.4 (8)	6.5 (7)	100 (108)

Notes:

a Blood test results before, at or within 1 month after the first-time registration in the Danish National Patient Registry.

Abbreviations: ACPA, anti-citrullinated protein antibody; ICD, International Classification of Diseases; IgM RF, immunoglobulin M rheumatoid factor; RA, rheumatoid arthritis.

Table S2 The blood test results of IgM RF and ACPA among confirmed ICD-10 M06 (other) RA diagnoses in the Danish National Patient Registry in the period 1977–2016 among the participants in the Danish Diet, Cancer, and Health cohort and derived from the Central Denmark Region hospitals

Confirmed ICD-10 M06 diagnoses, n=68	IgM RFa
ACPAa		Positive, % (n)	Negative, % (n)	Not available, % (n)	Overall, % (n)
	Positive, % (n)	2.9 (2)	1.4 (1)	0	4.3 (3)
	Negative, % (n)	(0)	26.5 (18)	0	26.5 (18)
	Not available, % (n)	10.3 (7)	26.5 (18)	32.4 (22)	69.2 (47)
	Overall, % (n)	13.2 (9)	54.4 (37)	32.4 (22)	100 (68)

Notes:

a Blood test results before, at or within 1 month after the first-time registration in the Danish National Patient Registry.

Abbreviations: ACPA, anti-citrullinated protein antibody; ICD, International Classification of Diseases; IgM RF, immunoglobulin M rheumatoid factor; RA, rheumatoid arthritis.