Thanks for the question.
There isn’t a great answer. Overall, after reading this literature, I am not convinced that contrast has any effect on renal function (with the massive caveat that none of the available literature can really answer this question).
Patients with low GFRs were included in a number of these studies, especially the larger reviews. In patients with worse baseline renal function, you are more likely to find a creatinine elevation on repeat testing, but that might be completely explained by the larger normal day to day variance in creatinine in CRF patients.
Right now, I think the answer is the same for everyone (including patients with GFRs <30). If you need a contrast study for an important diagnosis, you should get it. If the study isn’t necessary, you don’t get it.
The ways these two aspects of meditation are practised is that one begins with the practice of shamatha ; on the basis of that, it becomes possible to practice vipashyana or lhagthong . Through one's practice of vipashyana being based on and carried on in the midst of shamatha , one eventually ends up practicing a unification [ yuganaddha ] of shamatha and vipashyana . The unification leads to a very clear and direct experience of the nature of all things. This brings one very close to what is called the absolute truth. 
early 13c., "apparatus for weighing," from Old French balance (12c.) "balance, scales for weighing," also in the figurative sense; from Medieval Latin bilancia , from Late Latin bilanx , from Latin (libra) bilanx "(scale) having two pans," possibly from Latin bis "twice" + lanx "dish, plate, scale of a balance." The accounting sense is from 1580s; the meaning "general harmony between parts" is from 1732; sense of "physical equipoise" is from 1660s. Balance of power in the geopolitical sense is from 1701. Many figurative uses are from Middle English image of the scales in the hands of personified Justice, Fortune, Fate, etc.; . hang in the balance (late 14c.).