Autoantibodies in rheumatoid arthritis and their clinical significance

Table 3 Sensitivity and specificity of rheumatoid factor

	Rheumatoid factor (% positive patients)^*
Diagnosis	≥ 15 U/ml	≥ 50 U/ml	≥ 100 U/ml
Rheumatoid arthritis	66	46	26
Sjögren's syndrome	62	52	33
SLE	27	10	3
MCTD	23	13	6
Scleroderma	44	18	2
Polymyositis	18	0	0
Reactive arthritis	0	0	0
Osteoarthritis	25	4	4
Healthy controls	13	0	0
Sensitivity (%)	66	46	26
Specificity (%)	72	88 (92)^†	95 (98)^†

SLE, systemic lupus erythematosus; MCTD, mixed connective tissue disease. ^* Rheumatoid factor was determined by nephelogmetry in 100 patients with RA, in more than 200 patients with other rheumatic disease, and in 30 healthy controls. ^† Specificity when a diagnosis of Sjögren's syndrome can be excluded.