Background/Purpose: Rheumatoid arthritis (RA) is an autoimmune disease characterized by symmetric polyarthritis, rheumatoid factor positivity (RF) in the majority of patients, and bone erosions shown in radiographs. More recently, research has been conducted into anti-citrullinated peptides antibodies (ACPAs) to which greater sensitivity and specificity have been attributed than RF for diagnosis of RA. However, these antibodies have also been described in infectious diseases, particularly tuberculosis, placing the high specificity of the test in doubt. The aim of the present research was to study the presence of ACPAs in patients with tuberculosis (TB).

Methods: Patients with bacteriologically confirmed pulmonary tuberculosis, RA according to the American College of Rheumatology criteria, in addition to healthy controls (C) were included in the study. ACPAs were researched by two methods: anti-CCP (INOVA) and anti-MCV (Orgentec), in addition to RF by ELISA, in accordance with the protocol recommended by the manufacturers.

Results: The study was conducted in 50 patients with TB, 50 with RA and 20 healthy controls. Anti-CCP antibodies were found in 39 (78%) of the patients with RA, median titer:  128 U (interquartile interval:  24 to  233) whereas anti-MCV antibodies were found in  (50%) of the patients with RA, median titer of 21U (interquartile interval: 10 – 218). Of the patients with TB two (4%) had positivity for anti-CCP and anti-MCV and no patient in the control group tested positive for these antibodies. Sensitivity of anti-CCP for diagnosis of RA was 78% (CI: 63 to 88%) and specificity of 97% (CI: 89 to 99%) while the sensitivity of anti-MCV was 50% (CI: 35 – 64%) and specificity of 97% (CI: 89 to 99 %). RF was positive in  40 ( 80%) of the patients with RA, in 30 (60%) of those with TB and in 1 (5%) of the controls. Thus, sensitivity of RF was  80% (CI:  65 to 89%) and specificity of 55% (CI: 43 to 67%) for diagnosis of RA.

Conclusion: Our findings showed high sensitivity of anti-CCP and high specificity of both anti-CCP and anti-MCV antibodies for diagnosis of RA, even in a population with high incidence of tuberculosis. The higher frequency of positivity of ACPA in TB observed in previous studies may be attributed to methodological factors.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/antibodies-to-citrullinated-peptides-in-tuberculosis/