How can you tell the difference between rheumatoid and osteoarthritis in the absence of conclusive lab data?

Polyarticular...many: Rheumatoid is an inflammatory disease of the joint lining causing signs and symptoms of warmth/swelling/redness, typically affects many joints (polyarticular), usually both sides of the body (same joints), common in small joints of the hands except the distal joints of the fingers, typically marked morning stiffness of joints and muscles, no history of joint injury (trauma) to explain the pain...

Yes: Rheumatoid is a clinical diagnosis oa is a xray finding no lab test helps rule in either.