The validity of rheumatoid arthritis diagnoses in Finnish biobanks

Figures & data

Figure 1. Study flowchart. RA, rheumatoid arthritis; CRHC, Finnish Care Register for Health Care; seropos, seropositive; seroneg, seronegative; dg, diagnosis.

Table 1. Demographic and clinical characteristics of the study sample.

	N with data	All RA	Seropositive RA	Seronegative RA
Number of patients	233	233	118	115
Female (%)	233	160 (69%)	75 (64%)	85 (74%)
Year of diagnosis [IQR]	222	2005 [1996–2013]	2001 [1988–2012]	2008 [2001–2013]
Age at diagnosis in years [IQR]	224	50.0 [40.0–59.0]	46.0 [36.0–56.0]	54.0 [45.0–61.1]
Follow-up in years [IQR]	220	11.0 [4.3–22.0]	16.0 [4.5–30.0]	9.0 [4.0–16.0]
Diagnosed in rheumatology (%)	188	169 (90%)	79 (91%)	90 (89%)
Treated in rheumatology (%)	228	209 (95%)	103 (94%)	106 (95%)
Nr. of visits seropositive RA [IQR]	233	5.0 [0.0–25.0]	20.0 [6.0–31.5]	0 [0.0–3.0]
Nr. of visits seronegative RA [IQR]	233	2.0 [0.0–13.0]	0.0 [0.0–0.0]	11.0 [4.5–23.0]
Treated with DMARDs (%)	221	215 (97%)	110 (100%)	105 (95%)
Reimbursement for DMARDs (inclusion diagnosis specific) (%)	230	152 (66%)	61 (52%)	75 (66%)
Reimbursement for DMARDs (%)	230	219 (95%)	111 (95%)	108 (96%)
EULAR classification criteria positive at diagnosis (%)	136	79 (58%)	47 (72%)	32 (45%)
ACR classification criteria positive at diagnosis (%)	128	78 (61%)	41 (67%)	37 (55%)
ACR or EULAR classification criteria positive at diagnosis (%)	128	95 (74%)	49 (80%)	46 (69%)
EULAR classification criteria positive ever (%)	197	145 (74%)	89 (86%)	56 (60%)
ACR classification criteria positive ever (%)	176	131 (74%)	73 (77%)	58 (72%)
ACR or EULAR classification criteria positive ever (%)	195	164 (84%)	90 (89%)	74 (79%)
Highest RF ever [IQR]	189	13.0 [6.0–73.0]	75.5 [16.5–205.0]	9.0 [0.0–13.5]
Highest ACPA ever [IQR]	166	1.45 [0.0–126.0]	129.0 [7.0–340.0]	0.8 [0.0–1.6]
ACPA positive ever (%)	166	63 (38%)	55 (75%)	8 (9%)
Erosions in radiographs at diagnosis (%)	143	31 (22%)	19 (32%)	12 (14%)
Erosions in radiographs ever (%)	210	98 (47%)	66 (63%)	32 (30%)

ACPA, anti-citrullinated protein antibody; ACR, American College of Rheumatology; Eular, European League Against Rheumatism; DMARDs, disease-modifying anti-rheumatic drugs; RA, rheumatoid arthritis; RF, rheumatoid factor.

Figure 2. Positive predictive value of rheumatoid arthritis (RA) diagnosis in the Finnish Care Register for Health Care (CRHC) compared to chart review.

Table 2. Agreement between register-based diagnoses and chart review.

	All RA	Seropositive RA	Seronegative RA
At least one CRHC visit with RA
PPV (95% CI)	0.82 (0.76, 0.87)	0.75 (0.67, 0.83)	0.71 (0.62, 0.79)
NPV (95% CI)	1.00 (0.98, 1.00)	1.00 (0.98, 1.00)	1.00 (0.98, 1.00)
PLR (95% CI)	6.89 (5.21, 9.12)	9.48 (6.71, 13.39)	8.44 (6.12, 11.64)
NLR (95% CI)	0.01 (0.00, 0.04)	0.01 (0.00, 0.09)	0.01 (0.00, 0.10)
Accuracy (95% CI)	0.91 (0.88, 0.93)	0.92 (0.89, 0.94)	0.91 (0.87, 0.93)
Kappa (95% CI)	0.82 (0.77, 0.87)	0.80 (0.73, 0.87)	0.77 (0.69, 0.84)
At least one CRHC visit and reimbursement for DMARDs with inclusion diagnosis
PPV (95% CI)	0.89 (0.83, 0.94)	0.93 (0.84, 0.98)	0.79 (0.68, 0.87)
NPV (95% CI)	1.00 (0.98, 1.00)	1.00 (0.98, 1.00)	1.00 (0.98, 1.00)
PLR (95% CI)	16.44 (10.22, 26.44)	62.16 (23.50, 164.43)	16.29 (10.12, 26.22)
NLR (95% CI)	0.01 (0.00, 0.05)	0.02 (0.00, 0.12)	0.02 (0.00, 0.12)
Accuracy (95% CI)	0.96 (0.93, 0.98)	0.98 (0.96, 0.99)	0.95 (0.92, 0.97)
Kappa (95% CI)	0.91 (0.87, 0.95)	0.95 (0.90, 0.99)	0.84 (0.77, 0.91)
At least one CRHC visit and ACPA positivity
PPV (95% CI)	0.98 (0.91, 1.00)	0.96 (0.87, 1.00)
NPV (95% CI)	1.00 (0.98, 1.00)	1.00 (0.98, 1.00)
PLR (95% CI)	246.03 (34.78, 1740.19)	123.18 (30.96, 490.03)
NLR (95% CI)	0.02 (0.00, 0.11)	0.02 (0.00, 0.13)
Accuracy (95% CI)	0.99 (0.98, 1.00)	0.99 (0.97, 1.00)
Kappa (95% CI)	0.98 (0.95, 1.01)	0.97 (0.93, 1.00)

RA, rheumatoid arthritis; CRHC, Finnish Care Register for Health Care; PPV, positive predictive value; NPV, negative predictive value; PLR, positive likelihood ratio; NLR, negative likelihood ratio; CI, confidence interval; DMARD, disease-modifying anti-rheumatic drug; ACPA, anti-citrullinated protein antibody.

Figure 3. Positive predictive value of rheumatoid arthritis (RA) diagnosis in patients with reimbursement for disease-modifying anti-rheumatic drugs (specifically for RA).