got my lab results showing pretty low total tt (2,61 ng/ml)but normal free T (13,73pg/ml) on a quite high SHBG (77)!? is that normal? I would expect my free to be pretty low
That's not possible. The free testosterone test is suspicious. When I am in eastern Europe, I do not measure free testosterone because the tests there are unreliable and just give me random numbers. They can just determine if free T increases or decreases relative to the previous time, not the true value.
Yes, total T and SHBG tests are usually comparable between labs - I get similar values in US and in Eastern Europe.
Free T tests are unreliable and not comparable between each other, even in the same country. The values are comparable only within the same test to see if the free T increased or decreased from the previous time. They often get wrong even the "normal range".
Instead of a free T test, better use a Free T calculator: TruT calculator
When I was in Eastern Europe, they sent the free T test exactly to Germany and it came back in the middle of the "normal range", while in US it is at the low end.