i have mine done a lot. every two or three months.
and i just started lithium so, my previous test was in late december. i just had another a few days ago and another is scheduled for 2 weeks from the last test. my doctor will order them monthly after that if I continue Lithium.
i think insurance companies just dont want to pay all that money. lab tests are expensive for them. but luckily i have a vigilant doctor and I am assertive when it comes to my health.