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:

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

^bpatients 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;

^cpatients’ age at the time of rheumatoid arthritis diagnosis registration.

^dStata did not provide 95% CI in this case.

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