Most commonly, rheumatoid factor is used as a blood test for the diagnosis of rheumatoid arthritis. Rheumatoid factor is present in about 80% of adults (but a much lower proportion of children) with rheumatoid arthritis.
Most flights originating from the US have a 'two piece' limit for luggage - you can check two bags, and you pay extra per bag. This applies whether the flight is domestic within the US or international. Most flights that originate from outside the US have a weight limit for total checked baggage - a miserly 20kg/44lbs if you're traveling in coach class, 30kg/66lbs for business class and 40kg/88lbs for first class.
For most international travel (including domestic portions of such journeys), the liability limit is approx. $9.07 USD per pound ($20 USD per kilo) for checked baggage and $400 USD per passenger for unchecked baggage. Special rules may apply to fragile, valuable or perishable articles.