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.
Many luggage stores sell suitcases described as 'carry-on', but these suitcases are sometimes larger than the size most airlines will accept. The safe maximum size is 45, in the form of a 22 x 14 x 9 bag. Some airlines allow up to as much as 55, but most do not. Not only do luggage stores and manufacturers not always tell you if their bag is legally sized or not, but they also frequently mis-measure their bag.