RESEARCH - Clinical Utility of Anti-CCP Antibodies in a Population Tested for RF: Impact of Including Anti-CCP in the Diagnostic Criteria for Early RA

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ACR/ARHP Annual Scientific Meeting 2006

Washington, DC November 10-15

Abstract

Title: The Clinical Utility of Anti-CCP Antibodies in a Population

Tested for RF: Impact of Including Anti-CCP in the Diagnostic Criteria for

Early Rheumatoid Arthritis

Category: 17. RA - clinical aspects

Author(s): Rufus W. Burlingame1, Ana L. Bender2, A. von

Muhlen2, Henrique L. Staub2, Ines G. de Silveira2. 1INOVA Diagnostics, Inc.,

San Diego, CA; 2Pontifical Catholic University of Rio Grande do Sul School

of Medicine, Porto Alegre, Brazil

Presentation Number: 330

Poster Board Number: 330

Purpose: To determine the clinical utility of anti-cyclic

citrullinated peptide (CCP) antibody in a population where RF was ordered.

Both tests would likely be ordered together if anti-CCP antibody were

included in the criteria to diagnose early rheumatoid arthritis (RA).

Materials and Methods: Informed consent to test for anti-CCP was

obtained from 1025 consecutive patients for whom rheumatoid factor (RF) was

ordered at the University Central Hospital Laboratory. The RF requests

originated from primary, secondary and tertiary centers. A diagnosis was

obtained from the physicians without telling them the anti-CCP result. After

exclusion criteria were applied, 768 patients composed the final study

population.

Results: In this group, 132 people (17%) were diagnosed with RA. The

sensitivity for RA of anti-CCP was 62% while RF was 64% (Table I). Including

patients who were positive for either test increased the sensitivity of the

serologic tests to 71%. The specificity of anti-CCP was 97% compared to 90%

for RF, while it was 99% when both were positive (Table I). Anti-CCP was

statistically more specific than RF, while the difference in sensitivity was

not significant. Patients who were positive for both serologic markers had a

post-test probability of having RA of 86%, while RF yielded a 56% and

anti-CCP a 79% post-test probability of having the disease. Likelihood

ratios also favored anti-CCP over RF. Very low and very high levels of

anti-CCP reactivity were very strongly associated with the absence and

presence of RA, respectively.

Discussion: This is the first study of anti-CCP in a population

selected because an RF test was ordered. Including the anti-CCP results

yielded increased diagnostic probabilities that are statistically better

than RF alone in both early and established RA patients in this cohort.

Thus, anti-CCP is a clinically useful test in the patient population where

RF is ordered. 21% of the RF negative RA group, who are often difficult to

diagnose, were anti-CCP positive. Only 22 of the non-RA patients were

anti-CCP positive. Follow up studies on two groups of patients - those who

are not diagnosed with RA but are positive for anti-CCP, and those who are

diagnosed with RA but negative for both anti-CCP and RF - will yield further

insight into the diagnostic as well as prognostic utility of anti-CCP.

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