Mensa routinely conducts their own tests monthly , but will also accept standardized test scores , such as the SAT or ACT tests given at high schools in preparation for college .

The most common and widely accepted is the Stanford–Binet Intelligence Scales.

"The test measures five weighted factors and consists of both verbal and nonverbal subtests. The five factors being tested are knowledge, quantitative reasoning, visual-spatial processing, working memory, and fluid reasoning."

[en.wikipedia.org]

As much as I remember from my MENSA test (in Bulgaria), it was exclusively visual reasoning. Yet I have seen tests applying other methods like quantitative, lexical, and verbal reasoning among others. Results also vary sharply between tests - my MENSA result is 155, yet on other tests I have scored between 138 and 162. The only common thing is that 100 is the average in every test.
So in order to precisely compare the iq of two individuals, they should take the exactly same test under exactly the same conditions. Everything else is just speculation.