Diagnosis of rheumatoid arthritis: multivariate analysis of biomarkers.

OBJECTIVE: To test if a combination of biomarkers can increase the classification power of autoantibodies to cyclic citrullinated peptides (anti-CCP) in the diagnosis of rheumatoid arthritis (RA) depending on the diagnostic situation. METHODS: Biomarkers were subject to three inclusion/exclusion criteria (discrimination between RA patients and healthy blood donors, ability to identify anti-CCP-negative RA patients, specificity in a panel with major non-rheumatological diseases) before univariate ranking and multivariate analysis was carried out using a modelling panel (n = 906). To enable the evaluation of the classification power in different diagnostic settings the disease controls (n = 542) were weighted according to the admission rates in rheumatology clinics modelling a clinic panel or according to the relative prevalences of musculoskeletal disorders in the general population seen by general practitioners modelling a GP panel. RESULT: Out of 131 biomarkers considered originally, we evaluated 32 biomarkers in this study, of which only seven passed the three inclusion/exclusion criteria and were combined by multivariate analysis using four different mathematical models. In the modelled clinic panel, anti-CCP was the lead marker with a sensitivity of 75.8% and a specificity of 94.0%. Due to the lack in specificity of the markers other than anti-CCP in this diagnostic setting, any gain in sensitivity by any marker combination is off-set by a corresponding loss in specificity. In the modelled GP panel, the best marker combination of anti-CCP and interleukin (IL)-6 resulted in a sensitivity gain of 7.6% (85.9% vs. 78.3%) at a minor loss in specificity of 1.6% (90.3% vs. 91.9%) compared with anti-CCP as the best single marker. CONCLUSION: Depending on the composition of the sample panel, anti-CCP alone or anti-CCP in combination with IL-6 has the highest classification power for the diagnosis of established RA.

Assessing aspirin-induced attenuation of platelet reactivity by flow cytometry.

INTRODUCTION: Certain patient subpopulations do not respond to antithrombotic effects of aspirin and different approaches have been proposed to detect and define this so-called aspirin resistance. In this study, a methodological and clinical evaluation of a flow cytometric method for the detection of aspirin-induced inhibition of platelet cyclooxygenase (COX) is presented. MATERIALS AND METHODS: Platelet CD62p-antigen (P-selectin) expression was determined by flow cytometry after incubating diluted platelet rich plasma (PRP) with arachidonic acid (ARA). After establishing the method's technical characteristics, it was used to investigate 114 individuals (70 patients with atherosclerotic vascular disease under long-term medication of 100 mg aspirin daily, 29 age-matched patients with vascular disease without anti-platelet medication and 15 healthy volunteers). Data were compared to those obtained by the PFA-100 platelet function analyzer. RESULTS: Imprecision was between 3.3% and 13%. Sample storage at room temperature increased baseline activity of platelets already after 2 h. After ARA stimulation, the proportion of CD62p-positive platelets was considerably lower in aspirin-treated patients than in controls (median [lower-upper quartile]: 4% [3-6] vs. 50% [29-68], p<0.001). Only one aspirin-treated patient (1.5%) showed normal reactivity to ARA. In contrast to flow cytometry, PFA-100 analysis yielded normal results in 17% of aspirin-treated patients. CONCLUSIONS: The presented flow cytometric method can be used to monitor aspirin-induced inhibition of platelet COX. Aspirin resistance defined as failure to inhibit platelet COX is a rare phenomenon suggesting that most cases of aspirin resistance detected using the PFA-100 are caused by COX-independent mechanisms.

Pharmacokinetics of mycophenolate mofetil in patients with autoimmune diseases compared renal transplant recipients.

Mycophenolate mofetil (MMF), being effectively used as immunosuppressant in transplant medicine, has recently attracted interest as therapeutic agent for autoimmune diseases (AID). For these patients, no pharmacokinetic (PK) data are available. This study is an investigation of single-dose concentration-time profiles of 1 g off MMF in 16 patients with AID, including 10 patients with ANCA-associated vasculitis and 6 patients with systemic lupus erythematosus, and compares them with profiles of 16 renal transplant recipients (RTX). Mycophenolic acid (MPA) blood levels were measured by both HPLC and EMIT, and MPA-glucuronide was determined by HPLC. In AID, mean MPA concentrations at 12 h were significantly higher compared with RTX (4.1 +/- 3.27 versus 1.8 +/- 1.15 mg/L; P = 0.018), whereas peak concentrations were lower (P = 0.017). However, mean MPA-AUC at 12 h as well as at 24 h were comparable between both groups. In contrast to RTX, there was an association in AID between MPA trough levels at 12 h and at 24 h with AUC(0-12) (P < 0.05 and P < 0.01). MPA trough concentrations at 24 h provided an estimation of AUC(0-24 h) in both patient groups (P < 0.001 and P < 0.01; AID and RTX, respectively). Compared with RTX, MPA-PK seems to be less affected in AID by renal function. Inter-individual variability of PK parameters was high in both groups. These data indicate that there are differences of MPA-PK between RTX and AID. The use of therapeutic drug monitoring in patients with AID appears to be clinically practicable and may be valuable to optimize individual immunosuppressive therapy.