Efficacy of anti-ribosomal P protein antibody testing for diagnosis of systemic lupus erythematosus

OBJECTIVE: Anti-ribosomal P protein antibody (anti-P) is detected in a fraction of systemic lupus erythematosus (SLE) patients, especially with lupus psychosis, lupus nephritis, and lupus hepatitis. However, it has been unclear whether anti-P testing is specific for SLE. The current studies were designed to examine the efficacy of serum anti-P testing in diagnosis of SLE. METHOD: Multicenter retrospective study was performed with 102 SLE patients, 102 patients with non-SLE rheumatic diseases, and 100 normal healthy subjects, who gave informed consents. The diagnosis of SLE was confirmed according to the 1982 ACR revised criteria. Serum IgG anti-P was determined by ELISA using the C-terminal 22 amino-acids of ribosomal P protein conjugated to human serum albumin. The specificity and sensitivity of anti-P were compared with those of anti-DNA, anti-Sm, and anti-cardiolipin (CL) antibodies. RESULTS: Serum anti-P was positive in 38 of 102 SLE patients (37.3%), in 4 of 102 patients with non-SLE rheumatic diseases (3.9%), and in none of 100 normal subjects. Receiver operating characteristic (ROC) curve analysis revealed that anti-P provided higher AUC (area under the curve) than anti-Sm or anti-CL. Consistently, the sensitivity of anti-P (37.3%) was superior to that of anti-Sm (27.5%) and anti-CL (24.5%), but inferior to that of anti-DNA (51.0%), whereas the specificity of anti-P (96.1%) was superior to that of anti-CL (86.3%) and comparable to that of anti-DNA (96.1%) and anti-Sm (96.1%). CONCLUSION: These results indicate that serum anti-P testing might be an effective measure in diagnosing SLE, providing better diagnostic efficiency than anti-Sm and anti-CL.