OBJECTIVE: To evaluate the prevalence of baseline abnormalities in standard laboratory tests in patients with early arthritis and their impact on selection of disease-modifying antirheumatic drugs according to American College of Rheumatology (ACR) recommendations and/or of nonsteroidal anti-inflammatory drugs. METHODS: In three cohorts of patients with early arthritis (the ESPOIR, VErA, and Brittany cohorts), we evaluated the prevalence of anemia (hemoglobin<13g/dL in men and 12g/dL in women), leukopenia (<3500 per mm(3)), thrombocytopenia (<150000 per mm(3)), renal dysfunction (mild, creatinine clearance [CrCl]=60-89.9mL/min; moderate, CrCl=30-59.9mL/min; or severe, CrCl<30mL/min), liver cytolysis (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]>N or>2N), and systemic inflammation (erythrocyte sedimentation rate [ESR]>20 and C-reactive protein [CRP]>6). RESULTS: We evaluated 1393 patients (1018 women and 375 men). Anemia was present in 363/1366 (26.5%) patients, leukopenia in 18/1372 (1.3%), and thrombocytopenia in 13/1371 (0.9%). ESR elevation was seen in 50.4% of patients and CRP elevation in 62.7%. The level of AST was above normal in 4% and of ALT in 10% of patients. No patient had severe renal dysfunction, 5.6% had moderate renal dysfunction, and 42.6% had mild renal dysfunction. Among the 1094 patients who had undergone all the tests, only 18 (1.64%, 95% confidence interval, 1-2.64) had a formal contraindication to methotrexate therapy according to ACR recommendations (4 had leukopenia, 12 had high ALT levels, and 2 had high ALT and AST levels). CONCLUSION: Patients with recent-onset arthritis often have anemia, mild or moderate renal dysfunction, and abnormal liver function. However, fewer than 2% have laboratory test abnormalities contraindicating methotrexate therapy.