Serum Glucose -6- Phosphate Isomerase (GPI) Analysis In Patients With Rheumatoid Arthritis

Objective: To investigate the serum concentration of glucose-6-phosphateisomerase (GPI) in patients with rheumatoid arthritis (RA) and to analyze its value in diagnosis, disease activity assessment and prognosis.Method: The concentration of serum GPI in 30 patients with RA and 30 normal controls were investigated with sandwich ELISA method.The level of RF,anti-cyclic citrullinated peptide antibody (CCP) and anti-keratin antibody (AKA) were also investigated in RA patients.Other clinical records were collected,including CBC,urine analysis,ESR,CRP,ect.X-ray of hands and CT of lung were done and DAS28 (diease activity score,DAS) was calculated for all 30 patients.Based on the erosion of bone in X-ray,RA patients were divided into two different groups,with bone erosion (Sharp score≥1) and without bone erosion (Sharp score<1).We analyzed the association of serum GPI with other immunological markers and clinical records.Result: (1) GPI serum concertration in patients with RA were 0.84±0.78mg/L(X±SD).Significantly higher than that in normal controls(0.20±0.24mg/L,P=0.0003).Supposed serum GPI as a diagnostic indicator,receiver operating characterisitic curse (ROC) showed the optimun cut off level was 0.22 mg/L.At this point,the sensitivity was 73.3% and the specificity was 86.7% for RA diagnosis.(2) The positive rate of GPI in RA was 73.3%.This was not different from that of RF(P=1.0)and anti-CCP antibody (P=1.0)but was higher than AKA(P=0.003).(3) GPI concentration was positively associated with the level of RF(r=0.677,P<0.001﹚and anti-CCP antibody(r=0.58,P=0.001).(4) In Spearman analysis GPI concentraction was positively associated with ESR(r=0.579,P=0.0008),DAS28(r=0.589,P=0.0006)and immunoglobulin(r=0.43,P=0.016).It was negatively associated with plasma-albumin (r=-0.47,P=0.009)but was not associated with CRP,PLT,fibrinogen and morning stiffness.(5) No difference was found in GPI concentration between group with bone erosion and that without bone erosion.(6) The relationship between GPI and the extra-articular manifestations of RA was not statistically significant.Conclusion:(1)The concentration of GPI was significantly increased in RA.GPI is of high sensitivity(73.3%) and specificity(86.7%)in RA diagnosis when cut off level is set at 0.22mg/L.The positive rate of GPI was similar with that of RF and anti-CCP antibody.Therefore,GPI concentration might be of great importance in RA diagnosis.(2) GPI concentration was positively associated with ESR,DAS28 and immunoglobulin and was negatively associated with plasma-albumin.GPI might be an useful indicator assessing the disease activity of RA.(3) Neither the severity of erosion of bone nor the extra-articular manifestations of RA was associated with GPI.Further studies are needed to determine whether it is useful in RA prognosis.