Doctors dont like insulin tests because of the wide variation in norma test results, this means they can't fit you into the appropriate pigeon hole diagnosis.
There is a thing called HOMA-IR which gives an index between fasting insulin and glucose. You will probably have to self fund for this test and hunt out a lab that can do it.
Remember you can have normal HbA1c and fasting glucose with insulin resistance, so just low carbing may not break your IR.
You can infer IR from regular blood tests as IR pushes up Sodium, uric acid and blood pressure. Though many things also effect these numbers so not totally reliable.
This suject is also new to me but recent Fat Emperor podcast 41 covers this topic nicely.