Rheumatoid factor testing in Spanish primary care: A population-based cohort study including 4.8 million subjects and almost half a million measurements

• Published in: Reumatología clinica (Barcelona) Vol. 15; no. 6; pp. 350 - 354
• Main Authors: Morsley, Klara, Miller, Anne, Luqmani, Raashid, Fina-Aviles, Francesc, Javaid, Muhammad Kassim, Edwards, Christopher J., Pinedo-Villanueva, Rafael, Medina, Manuel, Calero, Sebastian, Cooper, Cyrus, Arden, Nigel, Prieto-Alhambra, Daniel
• Format: Journal Article
• Language: English
• Published: Elsevier España, S.L.U 01-11-2019
• Subjects: Artritis reumatoide; Atención primaria; Electronic health records; Especificidad, sensibilidad; Factor reumatoide; Historia clínica informatizada; Primary care; Rheumatoid arthritis; Rheumatoid factor; Sensitivity specificity; Rheumatoid factor; Artritis reumatoide; Atención primaria; Sensitivity specificity; Rheumatoid arthritis; Historia clínica informatizada; Primary care; Electronic health records; Especificidad, sensibilidad; Factor reumatoide
• ISSN: 2173-5743; 2173-5743
• DOI: 10.1016/j.reumae.2017.11.008

Rheumatoid factor (RF) testing is used in primary care in the diagnosis of rheumatoid arthritis (RA); however a positive RF may occur without RA. Incorrect use of RF testing may lead to increased costs and delayed diagnoses. The aim was to assess the performance of RF as a test for RA and to estimate the costs associated with its use in a primary care setting.
A retrospective cohort study using the Information System for the Development of Research in Primary Care database (contains primary care records and laboratory results of >80% of the Catalonian population, Spain). Participants were patients ≥18 years with ≥1 RF test performed between 01/01/2006 and 31/12/2011, without a pre-existing diagnosis of RA. Outcome measures were an incident diagnosis of RA within 1 year of testing, and the cost of testing per case of RA.
495,434/4,796,498 (10.3%) patients were tested at least once. 107,362 (21.7%) of those tested were sero-positive of which 2768 (2.6%) were diagnosed with RA within 1 year as were 1141/388,072 (0.3%) sero-negative participants. The sensitivity of RF was 70.8% (95% CI 69.4–72.2), specificity 78.7% (78.6–78.8), and positive and negative predictive values 2.6% (2.5–2.7) and 99.7% (99.6–99.7) respectively. Approximately €3,963,472 was spent, with a cost of €1432 per true positive case.
Although 10% of patients were tested for RF, most did not have RA. Limiting testing to patients with a higher pre-test probability would significantly reduce the cost of testing.
El factor reumatoide (FR) se usa en atención primaria para el diagnóstico de la artritis reumatoide (AR); sin embargo, un FR positivo puede observarse en sujetos sin AR, y su uso inapropiado puede conllevar costes y retraso diagnóstico. En este contexto, estudiamos la utilidad y costes del FR como test diagnóstico de la AR en atención primaria.
Estudio de cohortes retrospectivas basadas en datos de historia clínica informatizada de >80% de la población de Cataluña (SIDIAP). Se incluyeron sujetos de edad ≥18 años y con ≥1 medida de FR entre el 1/1/2006 y el 31/12/2011, sin diagnóstico previo de AR. El diagnóstico incidente de AR durante el año posterior a la medida de FR, y el coste por caso de AR fueron las medidas de interés.
495.434/4.796.498 (10,3%) pacientes tuvieron al menos una medida de FR 107.362 (21,7%) de estos fueron sero-positivos, de los cuales solo 2.768 (2,6%) fueron diagnosticados de AR en el año siguiente, comparado a 1.141/388.072 (0,3%) diagnósticos en sero-negativos. La sensibilidad del FR fue del 70,8% (IC 95%: 69,4 a 72,2%), especificidad 78,7% (78,6 a 78,8%), y valor predictivo positivo y negativo 2,6% (2,5 a 2,7%) y 99,7% (99,6 a 99,7%), respectivamente. El coste total estimado fue de 3.963,472€, alrededor de 1.432€ por caso de AR diagnosticado.
Aunque el 10% de participantes (casi medio millón de personas) fueron sujetos de medición/es de FR, la mayoría no desarrollaron AR. El uso de FR en pacientes con mayor probabilidad pre-test reduciría de forma significativa su coste.